A tradie has described how an unmarked police car travelling at high-speeds slammed into another vehicle during a pursuit that went horribly wrong in Perth’s south and has left an elderly man fighting for his life.

The serious incident unfolded while WA Police were pursuing a stolen grey Renault Koleos on South Street in Leeming about 10.50am on Monday.

A white Hyundai Accent was turning right onto Beasley Road via South Street, when it’s understood the driver — a man in his 80s — gave way to the stolen vehicle before pulling out in front of the police car, which was heading west on South Street.

The elderly driver had to be cut from his vehicle and rushed to Royal Perth Hospital where he is fighting for life in the intensive care unit.

The force of the impact resulted in the Hyundai’s engine being thrown into the air before landing near the roadway.

Two police officers — a man in his 40s and a woman in her 30s — were taken to Royal Perth Hospital as a precaution. They were discharged on Monday afternoon.

Tradie Owen Fallis, who was working near the scene of the crash, described the situation as “frightening” and recounted hearing the sound of a car’s engine sliding across the road.

“I turned my head around, it was nuts,” he said.

“The car’s front was totally ripped off, the engine was 30m at least away from the car. The smell of hot oil was in the air . . it was quite frightening.

”The heavy block of the engine, you could definitely hear that just get ripped out of the car and scrape across the floor, which I guess made it sound like a car was rolling towards us.”

“I thought that somebody (inside the white car) might have passed away, just based on the sheer impact and the sound . . just because it hit the front of the vehicle, the person inside, he visually looked okay but definitely will have injuries.

“I think the police officers got out of the car relatively quickly.”

Mr Fallis said members of the public rushed to the aid of the civilian who was injured, but that police and paramedics quickly locked the area down.

“The car that (the police) were in, the front end, it was definitely damaged, but not as much as the car that they hit. They were in a bigger vehicle . . . I don’t know what speed they were going, but it seems like they were probably going over 100km/h just based on the damage that was done,” he said.

“The officers that came out weren’t wearing the standard uniforms, so they must have been in some sort of undercover pursuit because there was about four other (police) cars following just as it had happened.

Both damaged vehicles were a large distance apart on South Street. The police car had a smashed windscreen and appeared to have taken out a sign, which was wedged underneath the vehicle.

WA Police said the stolen car at the centre of the pursuit was first spotted by officers on Albany Highway in Maddington about 10.35am.

The pursuit spanned several suburbs including Kenwick, Langford, Canning Vale before coming to an end in Coogee.

After the serious crash involving the police car, the stolen vehicle was tracked by the police air wing to a caravan park in the southern suburb, with the driver ditching the car and fleeing on foot.

A 27-year-old man was arrested on Cockburn Road and is assisting detectives. Police allege the car was stolen from a home in White Gum Valley about 3.10am on Monday.

The crash is being examined by officers connected to the major crash investigation section. The internal affairs unit have also been notified, which is standard protocol after a police vehicle crashes during a pursuit and does not suggest wrongdoing.

A police spokeswoman said any additional reviews of police actions “will be considered in accordance with WA Police Force policies and procedures”.

Authorities closed South Street westbound between Vahland Avenue and Beasley Road.

Main Roads said traffic was heavy in the area.