Girl dies after Illawarra high-speed crash

A teenage girl has died in a Sydney hospital after crashing a car while apparently racing through the streets of an Illawarra town.

The 17-year-old was cut from the wreckage of a Suzuki Swift and airlifted to St George hospital in critical and unstable condition on Friday evening.

It's believed she rolled her car on a corner of a Shellharbour road before smashing into a tree.

"Investigators have been told the Suzuki and a Ford Falcon XR6 were seen travelling at high speed through the sign-posted 50km/h zone shortly before the crash," police said.

"Officers are also investigating whether the cars were street racing."

A man, 22, who was driving the XR6, went to help the girl after seeing the crash, but was unable to free her.

He's been questioned by police and released pending further inquiries.

Specialist police are continuing their investigation and a report will be prepared for the coroner.