Two women are fighting for life after a police vehicle responding to an emergency collided with a Kia sedan in Sydney’s south-west, sending both cars through a fence and into separate homes.

Emergency services were called to Prairie Vale Road at Bossley Park about 12.20pm on Sunday after the two vehicles collided while the police car was travelling with its lights and sirens activated.

The impact sent both vehicles off the roadway.

They crashed through fencing before striking two different houses, leaving a major emergency scene across the residential street.

The driver of the Kia, a woman believed to be in her late 20s, suffered critical injuries.

NSW Ambulance paramedics treated her at the scene before she was taken to Westmead Hospital in a critical condition.

A second woman, believed to be in her early 50s and travelling as a passenger in the Kia, was also critically injured.

She was taken to Liverpool Hospital.

Two male police constables, both aged 24, were inside the police vehicle.

They sustained minor injuries and were taken to Liverpool Hospital for treatment and mandatory testing.

Despite both vehicles striking homes, police said no occupants inside the houses were physically injured.

The circumstances immediately before the collision are now the subject of a critical incident investigation.

Early reporting indicates the officers were responding to an emergency involving reports of a child on or near a roadway when the crash occurred.

The police vehicle had its emergency lights and sirens operating.

Importantly, there is no publicly established evidence at this stage that the Kia was being pursued by police.

Some early headlines described the crash as occurring after a “wild pursuit”, but the information released about the Bossley Park collision does not say officers were chasing the Kia.

That distinction is significant because a police pursuit carries a different operational and legal context from a marked police vehicle travelling under emergency conditions to another incident.

Investigators will now need to establish the movements of both vehicles, their speeds, traffic signals and right-of-way conditions, as well as exactly how the collision occurred.

A Critical Incident Investigation Team from Campbelltown City Police Area Command has been tasked with investigating the circumstances, with assistance from specialist crash investigators.

That investigation will examine the conduct of the police vehicle as well as the broader circumstances of the crash.

NSW Police said the investigation would be independently reviewed by its Professional Standards Command and overseen by the Law Enforcement Conduct Commission.

The declaration of a critical incident should not be interpreted as a finding that the officers involved acted improperly.

Under NSW Police policy, a critical incident can be declared when a police vehicle is involved in a crash causing serious injury or death, or when a crash arises from a police operation and somebody is seriously injured or killed.

The process is designed to ensure an incident involving police receives a higher level of scrutiny than an ordinary traffic collision.

Investigators are generally drawn from outside the command directly involved in the incident, while separate internal and external oversight mechanisms examine the investigation.

The Law Enforcement Conduct Commission is an independent statutory body with oversight responsibilities relating to NSW law-enforcement agencies.

Its involvement provides an additional layer of scrutiny where police conduct forms part of the circumstances being examined.

For the two critically injured women, however, the immediate focus remains medical.

The force of Sunday’s crash was sufficient to send two vehicles from Prairie Vale Road and into residential properties, demonstrating the extraordinary energy involved.

Images from the scene showed emergency crews around damaged vehicles and properties as investigators began documenting the crash area.

Police will likely seek CCTV, dashcam footage and witness accounts from motorists and residents who saw the vehicles in the moments before impact.

Vehicle data and the physical crash scene can also become important in reconstructing events.

Modern collision investigations can examine tyre marks, impact points, traffic-light sequencing, damage patterns and, where available, electronic information from vehicles.

The central questions will include how the Kia and police car came into conflict, whether either driver had sufficient opportunity to avoid the collision and how emergency-driving rules applied at the time.

Police vehicles operating under lights and sirens are afforded exemptions from some ordinary road rules in particular circumstances, but those exemptions are not unlimited.

Emergency drivers still have obligations to exercise appropriate care, and the precise circumstances matter.

That is one reason the investigation cannot be reduced simply to the fact the police vehicle had its lights and sirens operating.

Nor does the collision itself establish fault by either driver.

The Kia driver remains critically injured and there has been no suggestion that she has been charged with an offence.

No conclusion about criminal or disciplinary responsibility has been announced.

The crash comes as NSW Police continue to place significant emphasis on scrutiny of serious incidents involving police vehicles.

The force’s published safe-driving policy states that any police crash is subject to internal assessment, while crashes causing serious injury or death can trigger a formal critical incident process.

Where a critical incident is declared, the purpose is to preserve evidence, establish an independent investigative structure and ensure the actions of police are assessed against both road law and internal operational policy.

That process can continue for a considerable period, particularly where victims remain in hospital and investigators need expert crash-analysis reports.

Sunday’s collision is especially serious because two members of the public suffered life-threatening injuries.

It also caused substantial property damage and narrowly avoided injuries to people inside the houses.

For residents on Prairie Vale Road, the crash transformed an ordinary Sunday afternoon into a major emergency.

The fact that two vehicles left the roadway and struck separate homes means investigators will need to reconstruct not only the initial collision but the trajectories of both vehicles afterwards.

Those post-impact movements can help determine the angle and severity of the original crash.

The investigation will also need to establish exactly what emergency the officers were responding to.

Early reports described a call involving a child on a roadway or motorway.

Further official detail about that incident — including where the child was located and whether the emergency was still active at the moment of the crash — had not been publicly released by Sunday afternoon.

That is another reason caution is required with early descriptions of what happened.

Major incidents involving emergency vehicles often generate fragmented information in their first hours.

Witness accounts may be incomplete, emergency-service radio traffic may not be public and footage can show only part of the sequence.

The critical incident process is intended to resolve those gaps through formal evidence rather than assumption.

For now, the established sequence is limited but serious.

A police vehicle with emergency lights and sirens activated was travelling along Prairie Vale Road while responding to an emergency.

It collided with a Kia sedan.

Both vehicles then left the road, broke through fencing and hit homes.

The two women in the Kia were critically injured.

The two police officers suffered minor injuries.

No resident inside either property was hurt.

What remains unknown is why the two vehicles collided and whether any action by either driver contributed to the outcome.

Those questions now sit with the critical incident investigators.

Police have appealed for anyone with information or footage that could assist to contact Crime Stoppers.

Until the investigation establishes more, there is no basis to describe the Bossley Park incident as a police pursuit or to assign responsibility for the crash.

The immediate concern is the condition of the two women in hospital, while investigators begin the detailed work of establishing how an emergency police response ended with two cars embedded in suburban homes.