Scenes of disaray greeted first responders to the Cataract crash, about 7.45am Wednesday.

All three cars involved were badly damaged, with the engine from one - a blue Mazda - torn away and propelled about 20 metres down the road.

A 40-year-old woman spent 35 minutes compressed inside the Mazda wreckage with serious injuries to her chest, stomach and pelvis, as well as multiple lower limb fractures and a fractured wrist.

Firefighters used hydraulic equipment to cut her free from the driver's seat.

She was sedated and treated on the roadway, then flown by ambulance rescue helicopter to St George Hospital, in a serious condition.

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Early reports suggest the woman was driving westward when her car crossed onto the wrong side of the road and collided at high speed with an eastbound driver. A third car was also caught up in the crash.

From the eastbound cars, a female driver believed aged in her 20s was taken to hospital for assessment of minor injuries.

A male driver had minor cuts and abrasions from broken glass.

Veteran Illawarra paramedic Norm Rees said the damage caused by the crash was significant.

"I've been to a number of accidents, but here there was absolutely significant damage to all vehicles," Insp Rees said.

"The motor [from the Mazda] has actually been ripped out of the engine bay and was placed something like 20m away from the car.

"She was very, very lucky to survive."

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The road was closed between Wilton Road at Appin and the Princes Motorway at Cataract for more than two hours.

A police spokeswoman said inquiries into the collision were continuing.

"Initial inquiries suggest the blue Mazda has veered over to the incorrect side of the road," she said.

"Anyone who may have witnessed the collision, or who may have dashcam vision, is urged to contact Wollongong Police."

Wollongong Police: (02) 4226 7899