A steam train carrying a party of school children and a motor coach have collided at a level-crossing on the Swanage Railway in Dorset.
Only the driver was in the 52-seater coach when the crash happened
The 52-year-old driver of the coach, who is from Swanage, was flown to hospital with serious injuries.
The school children and the train driver were unhurt in the crash, which happened at about 1230 BST.
It occurred at Quarr crossing near Harman's Cross, south of Corfe Castle on the Isle of Purbeck.
Police, fire and ambulance services have been at the scene.
The coach driver, who was the only person in the 52-seater coach when it crashed, was freed by the Dorset Fire and Rescue Service at 1310 BST after being trapped under the wreckage.
He was then flown to Dorset County Hospital in Dorchester.
Ch Insp Rick Dowell, of Dorset Police, said: "A comprehensive forensic investigation is now taking place.
"It is too early to provide any definitive cause for the collision."
It is known that the level crossing is unmanned and there is no barrier or gate at the crossing, which leads down a track to a farm.
BBC viewer Lerida Arnold sent this image of the crash scene
A Swanage Railway spokesman said the crossing is controlled by flashing coloured lights.
Nick Brown, general manager at the railway, said the train was a 1950s British Rail standard class four tank engine, worth up to half a million pounds.
It was hauling five British Railway designed carriages.
He said between 30 and 50 passengers were on board the service from Swanage to Norden, including a party of 20 people, with the driver and fireman in the cab.
Mr Brown said the train would have been travelling at a maximum speed of 25mph and heading up a steep slope at the time of crash.
Arrangements were being made to remove the four rear-most carriages of the train and tow them back to Swanage railway station using another steam train.