Travel Somerset said northbound lanes had reopened but delays continued to affect motorists.

The farm supplies company said the truck was carrying “agricultural grade milk powder” for the Mole Valley.

A spokesman for Mole Valley added: “The fire was likely caused by a wheel or tire failure.

“The driver immediately called emergency services and the driver is safe.”

Northbound traffic is currently being diverted via the A38 and A39 at junction 23, reconnecting to the M5 at junction 22, with southbound diversion using the same roads in the opposite direction.

Stuck traffic will be released before the highways are opened, and delays are expected to continue.