A tradie has described how an unmarked police car travelling at high-speeds slammed into another car 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 on South Street in Leeming about 10.50am on Monday. WA Police were pursuing a stolen grey Renault Koleos through the area at the time.

A man in his 80s had to be cut from his white Hyundai Accent after it was struck by an unmarked WA Police vehicle.

The Hyundai was turning right onto Beasley Road via South Street at the time.

It is understood major crash officers are investigating if the Hyundai pulled out in front of the police car, which was was heading west on South Street.

The elderly driver was taken to Royal Perth Hospital under priority conditions. He was fighting for his life after being admitted to the intensive care unit.

The force of the impact resulted in a Hyundai’s engine being thrown into the air before it landed 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 as he worked nearby.

“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 in the vicinity of 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 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.

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

Main Roads said traffic was heavy in the area.