Investigators are probing the cause of a blaze that destroyed three ambulances outside East Surrey Hospital Monday afternoon.
Dramatic footage captured the fire and at least one explosion which forced the Redhill hospital to close to emergencies.
South East Coast Ambulance Service said that no patients or staff were on board the vehicles at the time.
An investigation is due to take place into what caused the fire, but the ambulance service said that the fire is believed to have started in an adjacent vehicle.
Witnesses described hearing loud bangs and "explosions" shortly after 2pm.
Images taken at the scene show smoke and flames near the hospital entrance.
Footage from the scene shows huge clouds of black smoke emerging from the vehicles.
Emergency services were called at 2.15pm.
Surrey and Sussex Hospital Trust announced at 4.15pm that the fire was "under control".
Patients had to be diverted through South East Ambulance Service, but Surrey and Sussex Healthcare NHS Trust said that the hospital is now "fully operational".
One witness described it as the "scariest" moment of his life.
Chris Priest, whose wife has just had a baby at the hospital, said that he heard the "bang and explosions".
Priest told Get Surrey: "My wife just had a newborn baby a couple of hours ago and we were in the delivery suite.
"I heard and bang and explosions, it was quite a noise and a shake. It sounded like a wardrobe crashing.
"We have been told to stay put, we would be leaving now."
He said that fire alarms were going off but staff seemed "calm".
Surrey Police evacuated staff and patients from the facility and put a cordon in place around the blaze.
Hazardous area response teams also attended the scene to assist Surrey Fire and Rescue Service.
Images of the burnt out vehicles were shared on social media.
Extensive damage looks to have been caused to the three ambulances.
A fully kitted ambulance costs £250,000.