Young boy injured in multi-car NSW crash

A young boy has suffered severe head injuries during a three-car crash in Sydney's southwest which left three others in hospital.

The boy, believed to be aged three, was injured while travelling in one of the cars which collided near the intersection of Hazel Street in Georges Hall on Tuesday evening.

He was taken to The Children's Hospital at Westmead in a serious condition, while his parents were taken to the same hospital suffering shock and minor injuries.

Crews worked to free the driver in the first vehicle for more than 30 minutes before he was taken to Liverpool Hospital.

The female driver in the third car was taken to Bankstown Hospital for mandatory testing.

It's not yet known what caused the crash, and police say the road will be closed for several hours as crash investigators examine the scene.