Watch as crews extinguish scrap cars in flames on Pacific Motorway

Around 30 firefighters between the NSW Rural Fire Service and Fire and Rescue NSW were called to the scene to find the crushed vehicles alight heading southbound.

Motorists reported a large cloud of thick, black smoke emanating from the trailer as the Prime Mover drove south around 12.45pm.

The driver, once alerted, pulled the rig to the side of the freeway and used an emergency telephone to contact authorities.

Five Fire and Rescue NSW (FRNSW) appliances, from Lake Macquarie and Central Coast stations, assisted by Rural Fire Service tankers, NSW Police and NSW Ambulance, rushed to the scene, where the driver managed to disconnect the burning trailer, containing a load of scrap metal.

An RFS spokesperson said that about 2.20pm crews had the fire under control but not completely extinguished.

Two southbound lanes of the M1 were blocked as firefighters sprayed the load with water and foam.

A decision was made at 2.30pm as crews then towed the trailer to nearby Old Maitland Road where they could better access the wreckage and extinguish the blaze.

"The load will be tipped out and be completely extinguished," the spokesperson told the Newcastle Herald.

There were no reports of injury arising from the incident.

It took fire crews almost three-and-a-half hours to douse the flames and complete mopping-up operations.

The cause of the fire is not yet known.