Roadside worker crushed by truck in Sydney's south

A roadside worker has died after a truck rolled over him in Sydney's south this morning.

Police say the 63-year-old asphalt worker was trying repair a bob cat bucket at a roadside worksite on Railway Parade, near Allawah train station just after 3.30am, when a truck drove forward and crushed him.

The Tregear man screamed as fellow workers ran to his aid, but he was caught in the rear wheels and couldn't be freed.

Emergency crews arrived a short time later and tried for four and a half hours to recover the man's body.

The truck driver, a 55-year-old Bringelly man, was treated for shock and underwent mandatory testing at St George Hospital.

He is assisting with the police investigation and Safework NSW is on scene interviewing witnesses.

A crime scene has been established near Allawah train station and traffic is heavy on Railway Parade, with drivers urged to avoid the area.

Pedestrian access at the train station's eastern entrance is also closed off while the crime scene is in place.