A driver is in a critical condition with head injuries after a car was ripped apart in a three-way crash, leaving debris strewn across one of Adelaide's busiest roads and causing an engine to smash through a window.

Key points: The driver of a BMW was taken to hospital in a critical condition

The driver of a BMW was taken to hospital in a critical condition Police said it was "miraculous" that another driver appeared unscathed

Police said it was "miraculous" that another driver appeared unscathed The crash has left debris strewn across the road

Police said a BMW sedan and a Commodore station wagon collided about 2:30am at the intersection of North East Road and Pitman Road at Windsor Gardens.

The driver of the BMW was rushed to the Royal Adelaide Hospital in a critical condition with major head and internal injuries.

The Commodore was ripped apart, with its engine flung across the road into the front of local business Rexel Electrical Supplies.

Part of the Holden Commodore in the crash that hit a business. ( ABC News: Troy Sincock )

"There's a motor sitting inside our back warehouse," said manager Scott Southworth.

"Debris is everywhere — it's like a tornado's hit it, that's what basically happened — it looks like a massive tornado.

"It's shocking, really. It's scary that this still happens.

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The BMW sedan was also wrecked in the crash, receiving major crush damage to its front section.

Police said a third vehicle, also a BMW, had been hit by debris but the driver was not injured.

They said it was "miraculous" that the driver of the Commodore had survived, and was being treated at the Royal Adelaide Hospital for shock.

"Go home, hug the family and buy a X Lotto ticket because she's probably the luckiest person today," Mr Southworth said.

"The female driver of the Commodore was able to step out of her vehicle and does not appear to have sustained serious injuries," Senior Constable Matt Brown said.

"The engine was ripped out of the car as well and landed about 30, 40 metres away."

ABC Radio Adelaide roving reporter Troy Sincock said debris was strewn across the road.

"The Commodore that was split in half is on the back of a tow truck … and people from the MFS are cutting portions of the car away," he said.

"One half of the car ended up on one side of the road and on the opposite side of the road is the engine to that vehicle, which has been flung through the window of a business, alongside a large portion of the front end of the car and one of the tyres.

"The debris is spread for about 100 metres down the road and literally looks like a movie scene."

The more damaged BMW involved in the crash is towed away. ( ABC News: Ben Nielsen )

Excessive speed to blame, police say

Police have been constantly battling to curb South Australia's road toll this year, which currently stands at 82 compared to 55 at the same time last year.

Inspector Damien Epps said speed was "definitely" a factor in the crash.

"We'll make allegations that the offending driver was travelling at a speed at least twice the posted speed limit for that location," he said.

"Obviously we are extremely frustrated and disappointed that people continue to drive and take significant risks, putting themselves in danger and also other members of the public at risk.

"They're scenes that nobody wants to see."

The Commodore hit a parked car at a local dealership.

One of the two BMWs involved in the crash with minimal damage. ( ABC News: Troy Sincock )

North East Road reopened about 9:40am after being closed in both directions between Sudholz Road and Fleet Avenue while Major Crash investigators examined the scene.

In a separate incident overnight, a 76-year-old man died in a crash at Morgan in the Riverland last night.

The local man was the only person in the car, which hit a pole on Fourth Street about 8:00pm, and police are investigating whether a medical episode led to his death.