More than 20 children have suffered minor injuries after a school bus crashed on Sydney's north shore.

Early reports suggest the bus collided with a car on Balfour Street at Lindfield around 11.50am (AEDT) on Friday, police say.

Twenty-nine children are being treated for minor injuries such as "bumps and bruises", Ambulance NSW says.

The driver of the bus and car have not been injured.

Police say they're yet to determine what caused the crash.

AAP svm/jjs/gd SYDNEY, March 8 AAP - More than 20 children have suffered minor injuries after a school bus crashed on Sydney's north shore.

Early reports suggest the bus collided with a car on Balfour Street at Lindfield around 11.50am (AEDT) on Friday, police say.

Twenty-nine children are being treated for minor injuries such as "bumps and bruises", Ambulance NSW says.

The driver of the bus and car have not been injured.

Police say they're yet to determine what caused the crash.