A man has witnessed a crash in which his wife and two young step-children were killed, the BBC understands.
Police were called to the A361 near Barnstaple in Devon at 08:25 BST after a car and a lorry collided.
The man was travelling in a separate vehicle and saw the crash unfolding behind him.
His family is believed to have been on holiday in Devon from elsewhere in England. The road was likely to be closed all day, police said.
Three ambulances, five rapid response vehicles and the air ambulance attended the scene near Barnstaple.
Devon and Cornwall Police said two children and a woman, believed to be their mother, had died as a result of the crash.
Road closures are in place between the West Buckland junction and the Lankey junction on the A361.
An investigation is under way and police have asked for witnesses to come forward.