Traffic is being diverted as emergency services work to free the trapped driver.

A man is dead and another is in a critical condition after two B-double trucks crashed on the Hume Hwy at Oolong, about 280km southwest of Sydney, on Thursday morning.

The first truck left the roadway and rolled near Pedell Ln, before a second B-double travelling behind smashed into the rear of the crashed truck about 1.15am.

“The male driver of one of the trucks died at the scene,” NSW Police said.

The second truck driver was found fighting for life when emergency services arrived at the scene.

He was still trapped in the wreckage at 6am, when NSW Ambulance told 7NEWS.com.au he was close to being extricated.

Three ambulance trucks, a helicopter, and RFS crews remained at the scene by 7am.

Investigations are ongoing, and a report will be prepared for the coroner.

All southbound lanes have been closed and traffic has been diverted to the Federal Hwy and Barton Hwy, police said.

One of two northbound lanes is also closed, according to Live Traffic NSW.

Vehicles over 25m will be parked, it said, adding that “ongoing police investigations are expected to take some time.”

“Allow extra travel time.”

Source Credit: 7 News

Photo Credit: Fire and Rescue NSW

Photo Credit: Fire and Rescue NSW