Concerns have been raised after a school bus taking children home caught fire - with the engine bursting into flames.

Parents said the same service broke down twice previously this week before the fire near Dorchester on Thursday afternoon which was witnessed by horrified onlookers.

It is alleged the door of the bus initially failed to open - and with smoke inside the bus from the fire some children were screaming as they were trying to get out.

The driver did manage to get everyone out safely and no-one was hurt while a replacement bus was laid on to take children home.

Bus operator Damory stressed that an investigation was underway and that its buses were serviced regularly. It said initial inquiries confirmed no issues with the doors.

The Damory service D3 was transporting children from the Thomas Hardye School and Dorchester Middle School when it started to emit smoke and caught fire, an onlooker said.

Pictures from the scene at Charlton Down show flames raging from beneath the vehicle.

It is understood passing motorists stopped to help at the scene.

A witness said: "The bus was stopped in Charlton Down and the children were evacuated by the bus driver.

"Initially, the door failed to open, but it did open and no-one was hurt, and the children were taken to a grass area near some houses. There were firefighters in attendance and two police vehicles arrived after the initial flames were put out."

They added: "I saw lots of smoke rising from around most of the bus. It was shocking to see. I am still in shock and so are many parents and children."

Parents say the same service - although it is unclear if it is the same bus - broke down twice this week with the vehicle apparently emitting smoke at one point.

One parent said: "It was shocking to see a bus that we trust to take our children in in this state."

The D3 service runs from the schools in Dorchester to Charlton Down and up the Cerne Valley via the A352 to Lyon's Gate.

Alex Chutter, Damory general manager, said: “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.”

Responding to concerns, Mr Chutter said: "Our buses are maintained and serviced regularly by our experienced engineering teams, however, like with all vehicles, faults can sometimes occur. The safety of our drivers and passengers is our first priority, and our team is fully trained to take appropriate action if situations like these arise - no matter how rare they might be.

“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. Early indications show very little damage to the vehicle.

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

Regarding the allegation of the bus door not initially opening, Mr Chutter said: "It’s not something we have been made aware of at the time of the incident, and the subsequent investigation so far has confirmed all entrances/exits are working as we'd expect them to be."

Dorset & Wiltshire Fire and Rescue Service said crews from Dorchester and Bridport were called to Herrison Road at 4pm.

The blue single decker Damory vehicle had a fire in the engine compartment, the brigade said.

It was extinguished by crews wearing breathing kits and using two hose reels. A small amount of engine oil was mopped up using environmental pads.

A spokesman for Dorset Police said: "We received a report from the fire service in relation to a vehicle fire in Herrison Road in Charlton Down. It was reported that a school bus was on fire but there were no reports of any injuries.

"Officers attended to assist the fire service and road closures were put in place. The vehicle was recovered and officers left the scene at around 6.15pm."

Damory operates a number of routes to various schools and colleges around Dorset on behalf of Dorset Council.

A spokesman for Dorset Council said: "Dorset Council takes the safety of all our school transport passengers extremely seriously. We are in contact with Damory and awaiting the results from their investigation into this incident."