Three children hurt in Sydney smash

Three young boys have been injured in a serious head-on car crash northwest of Sydney.

Police say the crash involving a Toyota Camry and a Nissan Patrol happened around 4.45pm on Sunday on Bells Line of Road at Kurmond.

Three boys, aged, six, nine and 12, who were passengers in the Toyota, suffered abdominal injuries.

The 12-year-old boy also suffered an injured wrist.

All three have been taken to Westmead Hospital.

"At this early stage it appears the male driver of the Toyota and the two occupants of the Nissan were not injured," NSW Police said in a statement.

Officers from the Metropolitan Crash Investigation Unit are en route to the scene and road closures are in place.