A birthday celebration at a short-term rental in Sydney’s south-west descended into what one terrified neighbour described as “a war” after gatecrashers allegedly sparked a violent brawl involving about 70 people and two teenagers were stabbed.

Police were called to a home on Zephyr Street in Austral shortly after midnight on Sunday following reports that two males had been assaulted.

Instead of finding the injured pair, officers arrived to a chaotic scene involving a large crowd outside the property.

Police say they encountered resistance from some of those present and were forced to use a range of force options, including OC spray, commonly known as pepper spray, as they attempted to bring the situation under control.

“It was a chaotic scene,” Liverpool City Police Area Command Detective Inspector Scott Houldin said.

“Police protected themselves with a variety of use of force.”

A neighbour who witnessed the violence gave an even more confronting description.

“I’d probably describe it as a war, you know, because there were so many people involved,” the witness said.

By the time officers began searching for the reported victims, the two injured teenagers had apparently left the immediate scene.

A short time later, police were called to Browns Road in Austral, where they found a 19-year-old man sitting inside a vehicle with stab wounds to his torso.

At about the same time, other officers located a 17-year-old boy in a second vehicle on Fletcher Street at Middleton Grange. He had suffered stab wounds to his thigh.

Paramedics treated both before they were taken to hospital in a stable condition.

The teenagers are believed to have been guests at the party before the gathering was disrupted by a group of alleged gatecrashers.

Police are now trying to identify those responsible for the violence from a crowd of dozens of young people, CCTV footage, mobile phone recordings and other evidence recovered from the surrounding streets.

Party spiralled after details spread on social media

What began as a private birthday gathering appears to have grown dramatically after information about the party circulated on social media.

Police believe a party was already underway at the Zephyr Street property when an uninvited group arrived.

According to Detective Inspector Houldin, the gatecrashers were met by a group of males at the front of the house.

Two of those males were the teenagers who later emerged with stab wounds.

Footage from the area captured the extraordinary disorder as the gathering spilled into the street.

Video broadcast by Australian television networks showed people moving through the neighbourhood as officers attempted to disperse the crowd. Police could be seen using OC spray amid the confrontation.

Separate CCTV footage showed an injured teenager moving through the street with a bloodied thigh.

Detective Inspector Houldin said he had viewed CCTV showing the scale of the chaos and confirmed the footage would form part of the police investigation.

For investigators, the immediate challenge is identifying individual offenders inside a large, rapidly moving crowd.

No arrests had been made as police continued their inquiries.

Officers have appealed for anyone with CCTV, dashcam or mobile phone footage from the area to come forward.

The request is particularly important because dozens of people may have recorded parts of the confrontation on their phones.

Even short videos captured before or after the main brawl could help investigators establish when particular groups arrived, identify vehicles or track the movements of those believed to have been carrying weapons.

Three knives seized near the house

Police established multiple crime scenes following the violence.

Three knives were recovered outside the home, along with other exhibits that will undergo forensic examination.

Investigators have not publicly confirmed whether any of the recovered knives were used to stab the two teenagers.

That question will form part of the forensic investigation.

Police will potentially examine the weapons for fingerprints, DNA and other material while comparing the physical evidence with CCTV and witness accounts.

The large number of people involved presents an obvious investigative problem.

Witnesses may have seen only fragments of the violence. Some partygoers may have fled as police arrived. Others may know the identity of those involved but be reluctant to assist investigators.

Detective Inspector Houldin said police encountered “some pushback” from people at the scene and that those involved were not assisting officers with their inquiries.

The lack of immediate cooperation makes digital evidence even more important.

CCTV from the rental property and neighbouring homes may provide a timeline of the arrivals and departures. Dashcam footage could identify vehicles used by the alleged gatecrashers. Mobile phone videos may show the confrontation from angles unavailable to fixed security cameras.

Police are also likely to examine social media activity connected with the party.

If invitations or location details were redistributed online, investigators may be able to establish how information about the private gathering reached people who were not originally invited.

Neighbours watched a quiet street erupt into violence

For residents of Zephyr Street and surrounding areas, the scale of the disturbance was particularly confronting.

Locals described the neighbourhood as normally quiet.

That changed suddenly as scores of people filled the street and the birthday gathering erupted into violence.

Television reports showed the disorder extending beyond the rental property itself, with people moving through neighbouring areas as police responded.

One report said members of the crowd crashed through neighbours’ fences while fleeing the scene.

For families living nearby, the violence was not contained inside a private party.

It spilled into the public street and surrounding properties.

The neighbour’s description of the scene as “a war” reflected not only the violence but the sheer number of people involved.

A brawl involving approximately 70 people creates a fundamentally different policing challenge from an isolated assault.

Officers arriving at such a scene must rapidly identify immediate threats, locate injured people, separate participants and protect themselves while attempting to determine who is armed.

In Austral, police initially arrived following reports that two people had been assaulted but could not locate the injured males at the house.

The victims were eventually found separately in vehicles at Browns Road and Fletcher Street.

That separation created multiple crime scenes and complicated the initial police response.

Investigators now have to reconstruct how each teenager moved from Zephyr Street to the locations where police found them.

The Airbnb party question

The incident has also renewed scrutiny of parties held at short-term rental properties.

The Zephyr Street home was being used as short-term accommodation when the birthday gathering was held.

Media reports described the property as a family-style getaway and said parties were prohibited at the accommodation.

The gathering was reportedly not originally advertised as a public event.

However, details eventually spread on social media and the number of people at the property grew.

The host also reportedly said the guests had asked for security cameras to be switched off before arriving.

That claim has not been publicly detailed by NSW Police as part of its formal account of the stabbing investigation, but if relevant footage or communications exist, they may attract interest as investigators reconstruct events before the brawl.

Airbnb maintains a global policy prohibiting disruptive gatherings and open-invite events.

The company introduced increasingly strict party restrictions after a series of serious incidents internationally and later made its party ban permanent.

The policy prohibits disruptive gatherings regardless of size and specifically targets open-invite parties promoted through social media.

But rules imposed by a booking platform cannot physically prevent an unauthorised crowd from arriving at a property.

That problem becomes particularly difficult when a private address is redistributed online.

A gathering may begin with a controlled guest list. Once the location is shared through group chats or social media, the original host can rapidly lose control of who is coming.

By the time neighbours or a property owner realise what is happening, dozens of additional people may already be travelling to the address.

The Austral brawl is an extreme example of how quickly such a situation can deteriorate.

Gatecrashers are central to the police investigation

The available police account points to the arrival of an uninvited group as the critical moment before the violence.

Detective Inspector Houldin said the alleged gatecrashers were met by males at the front of the property.

It was during the confrontation that the two victims are believed to have sustained their stab wounds.

Police have not publicly identified the attackers.

They have also not announced charges against any partygoer or alleged gatecrasher.

The investigation therefore remains at an important early stage.

Descriptions such as “gatecrashers” reflect the current police understanding of how the confrontation began, but criminal responsibility for the stabbings must still be established through evidence.

The recovery of three knives does not by itself identify who possessed them or whether they were used in the attacks.

Similarly, being present at the brawl does not establish that an individual participated in an assault.

This is why the CCTV review is likely to be painstaking.

Investigators may need to analyse footage frame by frame, compare clothing and physical features across multiple cameras and establish the movements of particular individuals through the crowd.

Mobile phone location and communication evidence could also become relevant if police identify suspects and obtain the necessary legal authority to examine devices or records.

Social media can turn a private address into a public destination

The spread of party details online is becoming an increasingly important issue for police, parents and short-term rental operators.

A private invitation can be copied in seconds.

One guest sends an address to a friend. That friend shares it with a group chat. Screenshots move between social media accounts. Within a short period, people with no connection to the original host can know the exact location and time of a gathering.

The risk is not limited to property damage or noise complaints.

An uncontrolled crowd can create conditions in which existing disputes, intoxication or the presence of weapons produce serious violence.

Police responding to the Austral incident were confronted with approximately 70 people, two stabbing victims who had already moved away from the original scene and a crowd that officers said was not fully cooperative.

That combination makes both emergency response and later criminal investigation more difficult.

There is also a significant impact on neighbours who had no connection with the party.

Residents can suddenly find dozens of strangers outside their homes, vehicles blocking streets and people moving through private property.

In the Austral case, the disturbance was serious enough that a witness compared the scene with warfare.

Police face a difficult identification task

The two stabbing victims have reportedly been cooperating with investigators.

But police still face the task of identifying their attackers among a large group of partygoers and alleged gatecrashers.

The passage of time matters.

Clothing can be discarded. Social media posts can be deleted. People can coordinate accounts of what happened.

At the same time, a large modern party can generate an enormous digital trail.

Phones record videos and photographs. Messaging applications preserve invitations and conversations. Home security cameras capture vehicles. Doorbell cameras record pedestrians. Dashcams may show people leaving the area.

The same social media sharing that may have contributed to the uncontrolled crowd could ultimately assist police in identifying those responsible.

Investigators have publicly appealed for community assistance rather than suggesting arrests are imminent.

That indicates the evidence-gathering phase remains critical.

Anyone who attended the party or recorded the brawl may hold material that appears insignificant in isolation but becomes important when combined with other footage.

A few seconds of video showing a person carrying an object, entering a vehicle or changing clothing could help establish a sequence of events.

Two teenagers in hospital, no arrests and major questions unanswered

The immediate medical outcome could have been considerably worse.

A 19-year-old suffered stab wounds to his torso, while a 17-year-old was stabbed in the thigh.

Both were taken to hospital in a stable condition.

Another teenager was reported by 7NEWS to have suffered lacerations to a hand during the violence.

But the criminal investigation is far from resolved.

Police need to establish who brought knives to the gathering, who used them, whether the violence involved multiple separate confrontations and exactly how the alleged gatecrashers learned of the party.

They must also determine whether the three knives recovered near the house can be directly connected with the injuries.

For the owner or host of the short-term rental, questions will also remain about how a property promoted as accommodation for a quiet stay became the centre of a 70-person melee.

For neighbours, the question is simpler: how could a private birthday celebration on a normally quiet street escalate so rapidly into scenes that left residents hiding inside and police using pepper spray?

The party was supposed to be a celebration.

By the early hours of Sunday morning, two teenagers had been stabbed, knives were scattered near the scene, multiple crime scenes had been established and detectives were beginning the difficult task of identifying attackers from a crowd of dozens.

No arrests have been made.

Police are urging anyone with CCTV, dashcam or mobile phone footage connected with the Zephyr Street brawl to contact Crime Stoppers.

For residents who watched the violence unfold outside their homes, the description that remains is the one offered by a shocked neighbour.

It was “like a war”.