A Royal Navy helicopter has crashed into a field in an incident police have described as “ongoing”.
Devon and Cornwall Police said emergency services were at the scene in Sourton Down near Okehampton in Devon.
A Royal Navy spokesperson said the incident happened just before 04:00 BST and an investigation was under way, adding “it would be inappropriate to comment further at this time”.
Prime Minister Sir Keir Starmer told the House of Commons it was a “deeply worrying time for the families” and more details would be released in due course.
Military helicopters often train in the area around north Dartmoor, which lies between the Royal Navy’s air bases at Yeovilton in Somerset and Culdrose in Cornwall.
The scene of the crash is also close to Okehampton battle camp, a military facility on the edge of Dartmoor which has been used for training Merlin helicopter crews from the Commando Helicopter Force.
The A386 between the A30 at Sourton Down and the A3079 Fowley Cross in Okehampton was closed at about 04:30 following the crash.
Staff at Sourton Cross Service Station, which is located near the scene, said the services were currently inaccessible.
At the scene, BBC reporter Richard Green said he had spoken to local witnesses who said they heard noises which sounded like “troubled mechanics” as a helicopter flew over.
He said the scene was “devastating” with wreckage visible in a field.
“A witness I spoke to described it as sounding not right as it flew over his house and it almost took the roof of his house off,” he said on BBC Radio Devon.
“He said it sounded like it was clearly in trouble and it sounded like it was mechanically failing.”
During Prime Minister’s Questions, Starmer said he was aware of the crash.
He added: “This will be a deeply worrying time for the families and more information will be set out as soon as possible.”