Three people died and others were left seriously injured when a coach overturned after colliding with a tree on an embankment.
The vehicle was travelling northbound on the A3 near Hindhead in Surrey at 11.50pm on Monday when it left the road between the Hindhead tunnel and the exit for Thursley. No other vehicles are believed to have been involved.
Three people aboard the 51-seat coach were declared dead at the scene and a fourth passenger was airlifted to Southampton General Hospital with life-changing injuries, Surrey Police said.
Other passengers, some of whom have serious injuries, have been taken to the Royal Surrey County Hospital in Guildford, St Peter's Hospital in Chertsey, St George's Hospital in Tooting, King's College Hospital in London, Frimley Park Hospital and Queen Alexandra Hospital in Portsmouth.
The road was closed in both directions shortly after the incident, and Surrey Police , Surrey Fire and Rescue and South East Coast Ambulance Service all attended the scene, along with collision investigators.
The coach is from the Merseyside area and Surrey Police is working with its counterparts at Merseyside Police, as well as with the coach company, to identify the passengers and notify relatives. Passengers are being taken to a rest centre which has been set up nearby by Waverley Council.
Surrey Police Assistant Chief Constable Jerry Kirkby said: "This has been declared a major incident and we are working with our colleagues from the other emergency services and other partner agencies to provide a co-ordinated response in line with agreed protocols. Our thoughts remain with the relatives of the dead and the injured at this time and we are working very hard to notify their next of kin."
The road is expected to remain closed for the several hours and diversions are in place. Motorists are asked to avoid the area until the road can be reopened.
Inspector Richard Mallett, speaking at the scene to Sky News, said the coach had been full and 53 passengers were thought to have been on board. He added: "We are confident that there is no-one left in the vehicle alive. Our colleagues from the fire and ambulance service with their specialist teams have been through the vehicle. It is a body recovery operation at this point here."
Surrey Police said a casualty bureau number had been set up and people concerned about passengers on board the coach should call 0800 056 0154.