The single-decker was ferrying about 20 pupils to West Calder High at 8.30am this morning on the A71 in Bellsquarry when smoke started billowing into the cabin.
One student said the driver had been struggling with the coach’s stuttering engine before the blaze. The cause is being investigated and no-one was hurt.
Brandon Mair, 17, told the Evening News: “We got picked up in East Calder and there was a smell like petrol. The driver pulled over at a layby and kept turning the engine off and on.
“We continued to West Calder and he stopped on the A71 and turned the engine off and on again. The bus was juddering and making weird sounds.
“Then at the roadworks the engine went off and on again and smoke and flames started coming out of the bus. It was about 10 or 15 seconds before the driver noticed and shouted for us to get off the bus.
“When we got off the bus, the driver said he kept getting a warning sign flashing on the dashboard.
“Some of the young kids at the front were panicking - they were upset.”
Dramatic footage captured at the scene shows flames leaping 20ft into the air from the back of the coach.
One mother said: “My child was on this bus and thankfully they are all ok.
And a fellow parent told the Evening News: “My daughter would’ve been on that bus if she hadn’t gone a different way to school.
“It’s frightening to think what could have happened. It looks like the fire started in the engine at the back and spread to the roof. Thank God no one was hurt.”
The coach belonged to Pumpherston-based E&M Horsburgh under a contract with West Lothian Council.
Another bus belonging to the same firm caught fire on Linlithgow High Street in March 2012. Only the driver was on board at the time and he escaped unharmed.
The Evening News reported in December on concerns from parents over the standard of an E&M Horsburgh coach on the school run from Winchburgh to Linlithgow Academy.
Mould was spotted on window ledges, water dripping from the ceiling, seats held together by tape and even a missing window.
Shocking photographs show considerable fire damage to the back and middle of the coach.
A spokeswoman for Pumpherston-based E&M Horsburgh said: “Everybody was evacuated from the bus safely. We’re trying to establish what happened.”
Asked if the single-decker had passed required tests, she added: “Of course it had, it wouldn’t have been on the road if it hadn’t.”
A replacement bus picked up pupils shortly afterwards to take them to school while the wreckage of the burnt-out coach was towed by 10.30am.
A spokesman for West Lothian Council said: “We understand from the operator that the bus driver noticed smoke from the rear of the vehicle and pulled over as a precaution allowing the pupils to depart the bus unharmed.
“Pupils were picked up shortly afterwards by another bus and taken to school.
“We’ve asked the bus operator to provide us with further details.
“Council officers visited the site this morning and will work with the operator to progress with an investigation.”