The truck collided with three cars on the M5 motorway east of Belmore Road just before 8.20am this morning.
Aerial footage from the scene appears to show a car almost split in two from the impact of the crash.
NSW Police said a child died at the scene, while another was taken to hospital for treatment.
“All four drivers – two women and two men – have been taken to hospital for mandatory testing and treatment of non-life threatening injuries,” police said in a statement.
Police hasve set up a crime scene and are appealing for information.
Live Traffic Sydney says all eastbound lanes are closed on the motorway at Riverwood.
It added that eastbound traffic is being diverted away from the scene via Belmore Road, Canterbury Road and King Georges Road.
RIVERWOOD: All eastbound lanes are closed on the M5 at Belmore Rd due to a multi-vehicle crash. Divert via Belmore Rd, Canterbury Rd & King Georges Rd to rejoin the M5. Traffic’s heavy, allow extra time. pic.twitter.com/ioRe1ZY7vo
— Live Traffic Sydney (@LiveTrafficSyd) November 26, 2019
Drivers are urged to allow extra time.
— more to come