A woman has amazingly survived an accident in which her car was crushed between two semi-trailers.

The crash closed the Great Western Highway at Blackheath in the Blue Mountains, as paramedics worked to free her from the wreckage.

The 34-year-old woman was left pinned by her legs in the tiny space left inside the KIA Hatchback.

One witness said: "Incredibly lucky to be alive, I've never seen a crash like it."

Her vehicle had been squeezed between two trucks, and left unrecognisable.

"Just a loud bang no brake noise, just an explosion like a car getting really squashed," another witness said.

Emergency crews arrived to find the woman from Darling Point, still conscious, and remarkably well - considering.

Paramedics say the woman sustained serious, but fairly minor injuries, given the circumstances.

After being freed from the wreckage she was transported by Careflight helicopter.

Dr Blair Mumford was on the flight and said: "She was fully conscious she could remember the whole incident.

"[She was] very relieved to be out of the car I think and I think very happy to be alive."

Emergency workers at Westmead were sent images of the crash site before she arrived at the hospital, and could not believe she was in a stable condition.

Police will be looking into the cause of the crash, and say it was an amazing escape.