Three lanes of the motorway were closed and National Highways reported delays of up to 94 minutes, with eight miles of congestion, as emergency services cleared the road.
John Richards, 47, was being driven to work when he filmed footage of the burning coach, which shows flames billowing from the back as thick smoke pours from two open doors.
A group of people are seen standing along the edge of the motorway near the coach.
Mr Richards, a landscape gardener based in Sutton, south London, told the PA news agency it was “quite unexpected to see something like that first thing in the morning”.
He managed to get ahead of the delays and said the coach fire “must have started about 10 or 15 minutes before we got there”.
Officials said the coach caught fire at about 7.50am between junctions seven and eight, in Surrey, which prompted the closure of lanes one, two and three.
We have been called to a coach on fire on the hard should of the M25, anti-clockwise between j7 & j8. We currently have 3 pumps in attendance, plus water carrier and unimog. The carriageway has been closed while we deal with the incident. Please avoid the area. pic.twitter.com/Zw42VMdNkH
— Surrey Fire & Rescue Service (@SurreyFRS) August 21, 2023
National Highways told the PA news agency that the anti-clockwise carriageway was blocked due to the fire on the hard shoulder.
The service said the initial delay was more than 90 minutes for some vehicles which was “reduced very quickly to 30 minutes and less than five miles congestion”.
Surrey Fire & Rescue Service tweeted that three pumps, a water carrier and a Unimog vehicle were on the scene.
National Highways said no-one was injured.
The lanes were gradually opened as the morning progressed and just after 1pm the fire service announced that all lanes had been reopened, with about one mile of congestion.
National Highways asked motorists to “please allow time for delays to clear”.