Injured school students from Baulkham Hills and Quakers Hill high schools were forced to climb out of a window of their school bus after it collided with a truck.
Two students were injured in the crash – one boy suffered a bleeding nose while another was treated for shock by paramedics, police said.
The bus, operated by Busways, had been travelling south on its school route on Quakers Hill Parkway about 4pm on Tuesday when a tipper truck pulled in front of it from the left lane, the evening controller from Busways, Michael Gowndar said.
Police are still searching for the truck driver, who sped off after the collision.
The bus door was so mangled the 10 students had to escape via the emergency exit, Mr Gowndar said.
"They were fairly shocked after the big bang."
The bus driver, a grandfather, was "really shocked" from the accident.
"He's going to have a couple of days off," Mr Gowndar said.
Busways sent two additional buses to the crash, but the students had already phoned their parents to pick them up, Mr Gowndar said.
"Everyone has mobile phones these days."
Police are appealing for anyone with information or who have seen a truck with the registration number BI08UK, to contact them.