Emergency services were called to Lane Cove Road at Macquarie Park at about 12.40am on Friday morning following reports of a crash between a Toyota Camry and a Honda Accord.

A female passenger of the Honda sedan was ejected from the side window of the vehicle when the two cars collided, and was run over by it when she landed on the road.

Witnesses to the incident stopped to help the woman, and had to lift the vehicle from on top of her before emergency services arrived.

She was treated at the scene by NSW Ambulance Paramedics, before being taken to Royal North Shore Hospital in a critical condition. The hospital said on Friday morning that the woman remained in a critical condition, but was stable.

The male driver of the Honda and his second female passenger were uninjured.

The driver of the Toyata and passenger, both male, were also taken to Royal North Shore Hospital but with non life-threatening injuries.

Officers from Ryde Police Area Command established a crime scene, which was being analysed by Crash Investigation Unit officers and other specialist police on Friday morning.

A police spokeswoman said that the Honda Accord appeared to have been T-boned in the incident, although the circumstances of the crash are still being investigated.

The southbound lane on Lane Cove Road at Fontenoy Road, and two of three northbound lanes, were reopened this morning just before 5am following closures surrounding the site of the crash.