This is the horrifying moment a school bus packed with up to 20 children burst into flames as children as young as nine screamed and shouted to get off.

The driver had no idea the underside of the single-decker bus was up in flames until motorists flashed their lights to alert him.

The footage shows students running off a bus in Dorchester, Dorset and running for shelter in case the vehicle exploded.

Until automobiles flashed their lights, the driver of the single-decker bus was unaware that its underside was ablaze.

Before firemen arrived 10 minutes later, one individual was seen using a fire extinguisher to put out the fire. The fire was suppressed by emergency personnel using a hose line and breathing apparatuses.

The Damory Coaches-operated bus was transporting students from Thomas Hardye School to Dorchester Middle School when a fire broke out.

All of the children were able to leave the bus with the assistance of members of the public.

The fire department arrived at Charlton Down in Dorchester about five minutes after the vehicle stopped.

Parents expressed indignation over reports that the identical car had broken down and been spotted ‘smoking’ only days before.

Parent of an eight-year-old boy on the bus Rachael Loco said: ‘My son was sat at the back of the bus and it was his friend who started shouting that they needed to get off the bus.

‘They could see the smoke and once the other kids knew what was happening they all started screaming and shouting.

‘None of them knew how to use the back exit so they had to go out of the front where they could see the smoke and fire.

‘They said that drivers behind the bus had been flashing to get it to stop and locals were quick to help, one even ran over with a fire extinguisher.

‘My son said that the bus had been smoking a couple of days before when they got to school and the morning of the fire it broke down.

‘I just keep thinking what if it had blown up?

‘I picked up my neighbour’s children too and they were all traumatised afterwards and really jittery.

‘To say that I’m upset would be an understatement, I just keep thinking how different the outcome could have been.’

Another parent Laura Foot said: ‘When I got there loads of the children were in tears and they all looked shocked.

‘My daughter now doesn’t want to go back on the bus.

‘I want to know what evacuation protocols the drivers and children are taught as my daughter was petrified stuck at the back of the bus, not knowing how to get off.’

Damory Coaches general manager Alex Chutter said: ‘I can confirm there was a fire on one of our coaches, transporting pupils from Thomas Hardye School and Dorchester Middle School. Nobody on board was injured.

‘The safety of our drivers and passengers is our first priority, and we are carrying out an immediate investigation to establish the circumstances behind this incident.

‘We arranged a replacement coach to transport those on-board to their onward destination and apologise for any inconvenience caused.’

The Dorset & Wiltshire Fire and Rescue Service said that two crews were called at 4pm yesterday (Thurs) and the bus had a fire in its engine compartment.

A spokesperson for Damory Coaches said today that 20 pupils were on the bus at the time of the fire. Alex Chutter, general manager for Damory, said: ‘Our buses are maintained and serviced regularly by our experienced engineering teams, however, like with all vehicles, faults can sometimes occur.

‘The coach in question was transported back to our depot, where it is being carefully examined by an independent vehicle inspector to establish the cause of the fire.

‘Once the cause is confirmed, I will take all possible steps to avoid any similar incidents in future.’