The ambulance was heading north on the freeway to Wollongong Hospital with a patient on board about 5.30am.

The ambulance was travelling at about 90km/h when a 4WD collided with the back of it just before it passed the Berkeley cutting.

Ambulance district officer Norman Rees said the impact dislodged everything in the back of the ambulance.

"It sent the officer (who was working on the patient) flying around," he said.

"He is being investigated for spinal injuries as a precaution."

The ambulance driver, patient and 4WD driver were not injured.

The NSW Fire Brigade rescue crew attended the scene to cut open the ambulance.

Operational commander Inspector Jay Bland said firefighters used the jaws of life to force the doors open and remove the glass panels from the doors.

"When the 4WD hit the back of the ambulance it caused the rails inside, which support the gurney, to buckle,'' he "The firies had to use a hydraulic device to push the rails down and release the stretcher.''