Photographs show fierce flames roar from the Westons cider vehicle on the motorway near junction 20 for Clevedon, Somerset. The motorway has been closed in both directions throughout this stretch but queues on both sides stretch for miles.
Emergency services dashed to the scene, which is on the northbound carriageway, at around 1.10pm and remain present.
The driver of the lorry is believed to have escaped the fireball unscathed, Bristol Live reports.
But northbound traffic is slow from junction 21 for Weston-super-Mare, Somerset.
Southbound traffic is congested from junction 18 for Avonmouth, Bristol.
A spokesperson for Avon & Somerset Police said: “A road closure is currently in place on the M5 northbound from between junction 20 (Clevedon) to junction 19 (Portishead) due to a vehicle fire. There are no reported injuries.
“Long delays are expected and motorists are advised to avoid the route.”
Three fire crews attended the blaze.
Darryl Hinksman, Head of Business Development at Westons Cider, said: “One of our vehicles did catch fire a couple of hours ago on the M5 near the exit for Clevedon.
“Thankfully the driver is unharmed and as far as we are aware there are no reports of any other injuries; we are currently making arrangements to bring the driver home.
“This is quite a new vehicle and at the moment we have no idea as to the cause of the incident.”