Five ambulance crews attended with a medical team and treated the boy at the scene before taking him to the Sydney Children's Hospital, where he was declared dead.

Police arrested the driver of the Corolla and took him to hospital for mandatory testing.

He was then taken to St George Police Station and charged with manslaughter, dangerous driving occasioning death, driving while disqualified and other traffic offences.

In a note to its community, the school said it had been in contact with the student's parents and was "working closely" with them.

"Our thoughts are with them at this very sad time ... Together as a community we will support each other through this tragedy."

Earlier in the day St George Police Chief Inspector Craig James said it was an "absolutely awful" incident.

"This was at 8.40am, school drop-off, so there were a number of kids being dropped off at school by mums and dads, there were teachers that ran out to this, general public that were in the area at the time."

A spokesman for the NSW Department of Education said the boy had previously been a student of Hurstville Public School and "was a much-loved member" of both school communities.

"The department, Sydney Technical High School and Hurstville Public School are working closely with all their students and staff to support them at this most difficult time. There is, and will be, ongoing extensive support in place for those impacted by this tragic event," he said.

He was refused bail to appear before Parramatta Bail Court on Saturday, September 7.

A crime scene was established and was examined by officers from the Metropolitan Crash Investigation Unit.

with Jenny Noyes