Four injured in NSW south coast crash

Two adults and two children remain in critical condition in Sydney hospitals following an accident on the state's south coast.

A car left the road and crashed into two trees as it travelled north on the Princes Highway at Wandandian about 8.30am on Thursday, police said.

Three occupants were trapped in the car and were rescued by ambulance crews after witnesses contacted emergency services and provided medical assistance until help arrived.

The driver, a 32-year-old woman and her front-seat passenger, a 32-year-old man, were transferred to Liverpool Hospital, while a seven-year-old girl and a nine-year-old boy were taken to Sydney Children's Hospital at Randwick.

All four remain in a critical condition, police said.

The car has been seized for forensic analysis and the driver will undergo mandatory drug and alcohol testing.