UPDATE: Police have issued an appeal over the suspected arson.
A police spokesman said: “We are keen to hear from anyone who saw anything unusual, particularly along the Tarka Trail between the Braunton Inn and Chivenor roundabout, in the early hours of the morning to contact police.
"We are also keen to speak to anyone who may have been working at the nearby Chivenor Business Park and may have been starting or finishing a shift there to call police with any information.”
Officers have this morning conducted house to house inquiries in the area.
A massive blaze which destroyed 40 vehicles, ignited a gas main and lit up the North Devon sky in the early hours of Saturday morning is being treated as arson, police have confirmed.
Fire crews were called to the region of Chivenor Business Park, near Barnstaple, just before 4am to reports of a small fire in the open.
However, it was obvious from the moment firefighters arrived on the scene that the fire was a major one, involving a number of vehicles at Chivenor Car Hire.
The incident was escalated and the initial two crews, one from Barnstaple and one from Braunton, were joined by a further two fire appliances from Barnstaple and Ilfracombe, the water bowser from Barnstaple and the incident command unit with a support vehicle from Ilfracombe.
Within half an hour of the call-out, it was confirmed that around a quarter of the vehicles in the compound, numbering 40 in total, were well alight.
Neil Blackburn, group commander for Devon and Somerset Fire and Rescue Service, said a joint investigation between the police and fire service was now under way.
"Our main concern was the governor gas assembly," he said. "We had to keep this burning because otherwise it could have caused a gas cloud which would have been a lot more dangerous."
As the fire continued to rage, parts of the nearby Royal Marines Base at Chivenor were evacuated.
Meanwhile Wales and West Utilities were summoned to isolate a gas main at the site.
By 5am, fire crews had requested the attendance of a compressed air foam systems appliance from Appledore.
A short time later, it was confirmed there were two separate seats of fire within a car compound containing approximately 40 vehicles and a gas main.
At 5.30am, following advice from Wales and West Utilities, fire crews were withdrawn from the site while further inspection of the gas main took place.
The smaller blaze was extinguished just before 6am, but the larger fire continued to escalate and was tackled with a compressed air foam systems jet and two crew members wearing breathing apparatus.
The gas main was isolated at 7.30am and the fire involving it was isolated. By 8am, fire crews reported that the incident was fully under control.
A spokesman for Devon and Somerset Fire and Rescue said it had been a big blaze: "This was a car compound containing several cars and minibuses, all severely damaged by fire. One gas main was compromised and involved in fire. An office and a portable building were also damaged by fire."
Fire crews are expected to remain at the scene all day.
A spokesman for the fire service said the cause was still being investigated.
The owner of the firm, who has run the business for 30 years, was said to be "distraught" after learning of the extent of the damage.