A horrified motorist desperately tried to flag down a school bus after seeing that it was being driven while on fire.
Pauline Gibson flashed her lights and beeped her horn and then ran screaming to the vehicle after it stopped north of Wick, Caithness.
Two minutes after the last of the students was evacuated, the coach was consumed by flames and destroyed.
It is thought the coach, owned by Stagecoach, suffered a mechanical fault and the flames were fanned by the strong winds that battered northern Scotland in recent days.
Scotland Fire and Rescue Service and Stagecoach are now investigating what caused the terrifying blaze on Monday morning.
The incident happened shortly before 9am when the 49-seater coach was still about five miles from Wick High School.
Miss Gibson, 44, who was driving to work on the A99, said: “I could see flames coming out the side of the bus and it was still moving. You could see the flames. I was just behind it.
“I flashed my lights and blew my horn. He stopped and I ran out screaming.
“The school children were coming out the bus. There must have been about 12 or 15 of them.
“Two minutes after they got off it was an inferno.”
“The school kids were upset and really shaken.
“I phoned 999. It was just minutes before it [the bus] was an inferno.”
“One of the boys was saying he was really warm and he just thought it was the heater.”
She added: “I’d hate to think of what could have happened.”
Gary Ridley, 49, saw his daughter, an S5 pupil, on to the bus near their home in John O’ Groats.
“I saw the bus leave. It was not going along very fast. I thought it was stuck in a gear,” he said. “My daughter called 15 minutes later to say it was on fire while on it. She saw fire was she was on the bus, out the side window. The bus driver got off, saw it was on fire, and told everyone to get off.”
A source close to the investigation said an electrical fault may have caused the fire and that strong winds may have fanned the flames.
A spokesman for Scottish Fire and Rescue service said: “We attended a coach fire at Quoys of Reiss (corr) farm at 08.59 on Monday morning.
“Two appliances from Wick were sent to the scene. Firefighters were met with a fire on a 49 seater bus and crews in breathing apparatus used two hose reel jets to extinguish the fire, which had destroyed much of the bus.”
A spokeswoman for Stagecoach said: “One of our vehicles travelling to Wick High School on Monday 12 January suffered a technical problem on the on the A99, in the Reiss area, at about 8.25am.
“The driver pulled over as a result of a warning light on the dashboard and ensured all passengers were able to alight the vehicle safely before calling the emergency services.
“Upon pulling over, the driver then detected smoke coming from the engine of the bus.
“No injuries were reported to any passengers or to the driver. A replacement vehicle was provided for the remainder of the journey.
“Safety is our absolute priority and we will investigate the cause of this incident as a matter of priority.”
She added: “We are still investigating the cause of this incident.”