Child Killed, Sibling Injured In Fatal Peak Hour Crash

A truck driver has been charged after a young boy was killed in a multi-car crash in Sydney's south.

Emergency crews were called to the M5, east of Belmore Road, in Riverwood at 8.20am on Wednesday.

A truck and trailer had ploughed into a Suburu travelling eastbound, before smashing into another two cars, sending debris flying across the road.

Two of the cars involved in the smash. Image: Steve Hart 10 News First

A 10-year-old boy who was in the backseat of the Suburu died at the scene, while his 13-year-old sister, who was in the front, was taken to the Sydney Children's hospital in a serious but stable condition.

The boy's mother, 31, and the drivers of the other two cars were treated for non life-threatening injuries.

All drivers involved have undergone mandatory testing.

The truck driver, 26, has been charged with a number of offences including dangerous driving occasioning death.

He was refused bail to front Bankstown Local Court on Thursday.

"As part of the investigation, the heavy vehicle has been seized, it will be subject to a mechanical examination and other factors that are relevant to a heavy vehicle," Acting Assistant Commissioner Paul Glinn said.

Image: Steve Hart 10 News First

He confirmed that factors such as speed, fatigue, the manner of driving and any use of a mobile phone will be examined.

"I can certainly confirm at this point that police at the scene have taken possession of a mobile phone which was in the heavy vehicle and that will be subject to forensic analysis", he said.

All eastbound lanes have now been re-opened on the M5 and diversions have been lifted after the crash was cleared, with heavy traffic beginning to ease in the area.

Anyone with information or dashcam footage is urged to contact Crime Stoppers.