Fatal Sydney crash accused behind bars

A man who allegedly fled the scene of a high-speed crash that killed a 12-year-old boy and left his family fighting for their lives is "deeply remorseful", his lawyer says.

Police say John Pagakis was behind the wheel of a Holden Commodore when it allegedly hit six stationary cars as he exited the M2 at Baulkham Hills about 7pm on Saturday.

A boy who was in a Holden Captiva died at the scene while a 36-year-old woman and a five-year-old girl were taken to hospital in a critical condition.

They are now in a serious but stable condition. The driver of the Captiva, a 38-year-old man, was taken to hospital for assessment. The injured are believed to be from a single family.

The driver of another car, a 65-year-old man, and his passenger, a 58-year-old woman, were taken to hospital with minor injuries.

The occupants of another four cars escaped unhurt but the drivers were taken to hospital for tests.

Pagakis allegedly fled the scene and was tracked by police to a Narraweena home in the city's northern beaches in the early hours of Sunday morning.

He was arrested and charged with 10 offences including dangerous driving occasioning death, failing to stop after a fatal crash and speeding at more than 45 km/h over the limit.

His lawyer, Peter Proctor, did not apply for Pagakis's release at Parramatta Local Court on Monday morning and bail was formally refused.

"He's deeply remorseful and it's a tragic case and ultimately justice will be done," Mr Proctor told reporters outside court.

Mr Proctor said the reality of the situation was now sinking in "with great difficulty" for Pagakis.

The 34-year-old was ordered to reappear on May 2 in the same court.