Witnesses have told police they found the 17-year-old lying by the side of the road on Northcliffe Drive, near the intersection of Lake Heights Road, shortly after 1am.

On Sunday, the girl’s sister took to social media with an impassioned plea for assistance to locate the driver.

‘‘Last night my younger sister... was walking home alone from Warrawong to Berkeley,’’ she wrote.

‘‘She was found unconscious on Northcliffe Drive.

''She may [have] been abused or [involved] in a hit and run between 12.30 and 1.30. 

‘‘Any information please let me know or if she has taken anything.’’

Police said they were investigating the possibility that the girl was struck by a vehicle and the driver left the location.

The 17-year-old suffered serious head injuries, police said.

The girl was treated by NSW Ambulance Paramedics before being taken to Wollongong Hospital, where she remained on Sunday in Intensive Care.

The girl’s sister said she was suffering from ‘‘bleeding on the brain’’.

Police spoke to a number of witnesses in the neighbourhood, who described hearing a loud noise shortly before discovering the girl on the roadway.

Northcliffe Drive resident Lola Smith said she heard a ‘‘slight bang’’ around the time the girl was hit.

‘‘It’s awful,’’ she said. ‘‘We haven’t had anything like that along here before.

‘‘I just hope the girl survives.’’

Specialist officers from the Crash Investigation Unit also attended and examined the scene.

Traffic was being diverted while police investigated on Sunday morning.

Inquiries into the matter are continuing and police are appealing for anyone who may have witnessed the incident, and has not yet spoken to detectives, to come forward.