A man has been killed and another seriously injured after a smash on one of Sydney's busiest roads this morning.
A B-double truck reportedly ran over a station wagon before overturning on the M7 at Quaker's Hill in Sydney's west at around 9.10am this morning.
The station wagon driver died at the scene and while the truck driver was airlifted to hospital after the collision, police said.
The truck driver, 50, suffered severe leg injuries when his vehicle reportedly collided with the station wagon, which had stopped in the breakdown lane.
Motorist Tony McGrath described the crash scene as "gruesome".
"It's pretty ugly — it appears that the dump truck has lost its trailer and rolled over and over again by the looks of the things," he said.
"If you saw the cabin or the truck you'd wonder how the hell anybody would get out of that."
Nearby resident Kerry Brinsdon said she heard the crash from around 500m away.
"All the traffic is blocked up — there were sirens everywhere," she said.
"Traffic in the opposite direction was backed up because other truck drivers were stopping to see if they could help."
Mr McGrath said the crash had closed all the southbound lanes of the M7.
"The cabin of the truck is completely crushed the trailer has come away from the dump truck itself and is on its side in the middle lane," he said.
"Southbound on the M7 is completely closed and there's a huge traffic jam."
Traffic travelling in the direction of Plumpton was being diverted to Sunnyholt Road, east of the crash site, the RTA said.