Fire crews have extinguished a semi-trailer that exploded in flames overnight, blocking the Pacific Highway at Pimlico.

The B-double caught fire in the south-bound lanes of the highway outside Pimlico, south of Ballina, just before 11.30pm.

The truck and trailer were carrying six tonnes of aerosol spray cans, which ignited, causing large explosions at the scene.

The truck driver and another motorist made it to safety as the fire took hold.

The semi also contained bags of gravel and cane mulch.

Three Fire and Rescue NSW (FRNSW) trucks from Ballina and a Hazardous Materials (HAZMAT) appliance from Goonellabah were joined by four Rural Fire Service tankers, NSW Police and NSW Ambulance at the scene.

The firefighters extinguished the truck fire and numerous spot fires caused by the exploding cans.

They also deployed an absorbent barrier to protect the environment from liquid run-off and decanted 400 litres of diesel fuel from the burning rig, which was destroyed in the fire.

Traffic flow was limited to one lane north-bound during the three-and-a-half hour operation.

The cause of the incident has not yet been determined.

Live Traffic shows the Pacific Highway is clear at Pimlico.