A driver has died in a crash involving four trucks on a busy motorway in the NSW Hunter Region.

The trucks, including a petrol tanker, crashed about 2.45pm on Tuesday on the M1 Pacific Motorway near Mandalong Rd at Morisset, trapping one of the drivers.

The man, who has not yet been identified, died before emergency services arrived at the scene.

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7NEWS chopper footage shows two trucks at the front collided in a rear-end crash, while the other two trucks are parked across the lanes.

NSW Ambulance said paramedics treated three drivers at the scene for minor injuries.

Police confirmed a second driver, a 57-year-old man, was not injured.

A rescue helicopter was seen landing at the scene to assist emergency crews.

A crime scene has been established and is expected to remain for some time, causing ongoing traffic disruptions.

All southbound lanes of the motorway at Morisset have been closed, with significant delays in the area.

Drivers are being urged to avoid the area and seek alternative routes.

“Traffic is heavy so motorists are advised to allow plenty of extra travel time,” NSW Transport Management said.