An ambulance from Hertfordshire on a 999 call was destroyed on the A1(M) in Bedfordshire on Sunday night.
The East of England Ambulance Service vehicle from Letchworth was responding to a call from Dunton at 2205 GMT.
The crew, on the A1(M) northbound carriageway near Astwick, noticed smoke coming from the front of the vehicle.
They pulled over and called for assistance but flames engulfed and destroyed the vehicle. An investigation into the cause of the fire has started.
Ambulance service spokesman Gary Sanderson, who attended the incident, said: "First and foremost this must have been a very traumatic incident for the crew to deal with.
"Their quick thinking no doubt saved any injuries to themselves and other road users.
"They were able to park the vehicle in a safe place and alert on-coming traffic of the situation."