Two young children are fighting for life after being struck by a car on a major highway in Sydney’s southwest.

Emergency services were called to the intersection of Joseph St (Cumberland Highway) and Gilbert St in Cabramatta about 3.15pm on Wednesday.

The children are believed to be aged 1 and 5. They were treated at the scene before being rushed to The Children’s Hospital at Westmead in a critical condition, NSW Ambulance said.

7NEWS helicopter footage shows a black car on its side beside the roadway following the crash, while multiple ambulances and emergency crews work at the scene.

Paramedics and other emergency personnel can be seen treating patients, with privacy screens erected on the road.

All southbound lanes of the Cumberland Highway have been closed between John St and Cabramatta Rd West.

Motorists are being urged to avoid the area and use alternative routes.

More to come …