One person is believed to have died and more than 30 people have been injured, three seriously, after a crash between a double becker bus and a car, the Ambulance Service has said.
Some people are believed to have been trapped in the wreckage after the bus reportedly hit a car in the village of Alton, Staffordshire, came off a bridge over the River Churnet before careering into a garden.
Reports suggest that there has been one fatality on the bus which was carrying about 70 foreign visitors returning from a day trip at Alton Towers theme park.
According to Sky News, 44 people were uninjured in the crash, with 26 still "not accounted for" - some of these are those who have been transferred to hospital.
West Midlands Ambulance Service spokesman Murray McGregor said: "It’s very serious. We have got lots of resources there."
Two helicopters, eight ambulances, four rapid response cars, a doctor and two first responders have been sent to the scene.
Emergency services were called to Station Road, Alton, just before 6pm.
The crash happened about half a mile from the Alton Towers theme park.
Mr McGregor said initial reports had suggested seven people were trapped in the wreckage and up to 30 walking wounded.
"It’s clearly a very big incident," he said.
Patients were being airlifted to a number of hospitals, he said. Three were taken to the University Hospital North Staffs, at Stoke-on-Trent, another to the trauma unit at Selly Oak Hospital in Birmingham, and another to Nottingham.
A spokeswoman for University Hospital Birmingham NHS Trust said: "A 20-year-old woman has been airlifted into Selly Oak Hospital"
It is believed the woman is in a "critical" condition.
Initial reports suggest there are patients with head injuries. Exact details are still coming through to us," said Mr McGregor.
The village is used by traffic going to the theme park. "The roads are quite narrow in many places."
"Exact details can’t be confirmed at this stage. The ambulance crews’ priority is dealing with the patients first and foremost."
He said they could not comment on reports that the bus may have been carrying foreign workers.
Bradley Ford was in a nearby field when the crash happened and was one of the first people on the scene.
He told the BBC he thought the bus was carrying about 50 foreign workers from a farm near Peterborough on a day trip to the Alton Towers theme park, which is about half a mile away.
"I heard this massive crash and rumble - crunching metal. It sounded initially like a thunderstorm, but then we heard shouts and screams," he said."
Mr Ford, who runs the Alton Bridge Hotel on Station Road, added: "From what I could see a coach had crashed at the hill and ploughed through a neighbour's garden.
"It ploughed through two cars parked in a driveway. One of them was bouncing down the road, the other must have flown along with the coach.
"It must have dropped about twenty feet. It was on a slope, it's diagonal, not head-first.
"There were people climbing out of the fire exits on the bus. The majority of the people were walking wounded. Probably half a dozen had serious injuries.
"There's a bad bend at the bottom of the hill which is in line with the neighbour's driveway.
"They couldn't have managed to take the corner and had no choice but to go through."
Mr Ford said he used his first aid training to try to help the crash victims, getting nearby residents to bring bandages and blankets.
"With the theme park kicking out, there's a lot of traffic on the roads, and they're all being diverted," he said.
"Police and fire crews are cleaning up the rubble - the fire crews have stabilised the vehicles."
Mr Ford said he thought fire crews had removed everyone from the wreckage.
A spokeswoman for Alton Towers said: "A private hire coach from Luton left the road at the bottom of the Alton Bank. All of the emergency services are in attendance including the air ambulance.
"All roads through Alton village are currently closed. Alton Tower’s priority is to redirect traffic leaving the resort through Farley which was implemented immediately to ensure no further build up of traffic which might impede the emergency services.
"Alton Towers first responders were on the scene within minutes of the accident occurring and the resort is now providing assistance with casualties who we are bringing back to our facilities.
"We have no information as to the severity of the injuries."