A child was killed when a coach carrying pupils returning from an end of term day trip to a zoo flipped on to its roof and plunged down an embankment in Somerset.

Twenty-one passengers were taken to hospital by vehicles and a helicopter, some with serious injuries. Others were treated at the scene.

The coach overturned on its roof and slid 6 metres (20ft) down an embankment. An off-duty firefighter was following the coach and began helping the children and adults from the vehicle. Some of the passengers were trapped in the coach and had to be freed by firefighters.

Many of the children who did not need hospital treatment spent around five hours at a makeshift rest centre before being ferried back to Minehead middle school where parents gathered to pick them up.

Ch Supt Mark Edgington of Avon and Somerset police said: “Shortly before 3pm this afternoon, emergency services were called to a collision involving a coach on the A396 at Cutcombe Hill, in Exmoor.

“Approximately 60 to 70 people were believed to be onboard. A major incident was declared, with police, fire and ambulance services dispatching crews to the scene.

“A number of other people have presented or been taken to hospital, some of them with serious injuries. This includes two children who were taken to hospital by air ambulance. An investigation into the cause of the incident will be carried out.”

He asked people not to speculate on the cause of the crash, saying it would add to the distress of “the families, staff and the driver”.

Wayne Darch, deputy director of operations at South Western ambulance service, said it sent 46 resources to the scene. He said the child, who has not been named, died at the scene.

Gavin Ellis, the chief fire officer for Devon and Somerset fire and rescue service, said it sent 60 personnel. “Our crews carried out a number of extrications and rescues in extremely difficult circumstances,” he said.

The area the crash happened in is heavily wooded and the embankment the coach went down steep.

Ellis said: “This was a very complex and technically difficult operation. I’m grateful to the off-duty firefighter who was travelling behind the coach at the point of the crash who was able to start making immediate effect to release those casualties from the bus.”

The coach company Ridlers said one of its 70-seat vehicles was involved.

Peter Prior-Sankey, the director of Ridlers, said: “We were made aware of an incident involving one of our 70-seater vehicles at about 3.15pm this afternoon.

“While we wait for further information from police and other emergency teams, our hearts of course go out to the school pupils and to our driver. We will be doing everything possible to understand what has happened.”

Roger Weather, a farmer in Wheddon Cross, told how he helped direct the families of those on board to a makeshift “care centre” set up by emergency services teams at the village pub, The Rest and Be Thankful Inn.

Some parents went there to try to find their children. Weather said: “The poor parents were very anxious and desperately trying to find out where their children had been taken.

“It’s very rural here, so places are hard to find. I did what I could to direct people to where they needed to be.

“As a village, you just don’t expect this kind of thing to happen on your doorstep. You hear about these things happening in the media, but always somewhere else. “Today it happened here. Everyone in the village in a state of complete and utter shock.“

Heidi Alexander, the transport secretary, said: “My thoughts are with all those involved. I am receiving regular updates on the situation.”