Man dies after teens' fiery car crash

An 18-year-old critically injured in a high-speed, single-vehicle, fiery crash in Sydney has died in hospital as four other teens continue treatment.

The man was a back-seat passenger in the sedan allegedly driven by a 16-year-old that hit a tree in Cammeray on the city's north shore on Sunday afternoon.

He'd been treated for head and chest injuries in Royal North Shore Hospital but died on Thursday, police said on Friday.

The driver and three other passengers - two girls aged 16 and two boys aged 17 - are in hospital in a stable condition.

The crash occurred after police twice gave chase and then terminated pursuits of the sedan.

After leaving the road and striking a tree, it burst into flames.

Police said the car, which was owned by the 18-year-old, had been connected to reports of a fight between teens in nearby Wollstonecraft.

A critical incident team from Blue Mountains Police Area Command is investigating the circumstances surrounding the incident under Strike Force Mulvany.

The investigation will be subject to independent review.

Police are appealing for anyone with dash cam vision or who witnessed the crash to come forward.