A major road closed all day following an explosion has re-opened - and while police have ruled out any link to terrorism they said they "may never find out what the source of the explosion was".
North Yorkshire Police said the six-mile stretch of the A1 motorway - including the part of the road running adjacent to Marne Barracks, near Catterick - was closed for so long due to reasons including "the current threat to UK security" and a vehicle "seen in suspicious circumstances" outside the barracks.
Police said the noise of an explosion was reported by staff from Marne Barracks, near Catterick, at 3am.
Officers carried out extensive searches in the area where the explosion was reported but found no obvious signs of an explosion.
During the course of the day, eight members of the public came forward to report hearing what they describe as an explosion in the area.
No reports of any injuries were received, police said.
The searches involved specially trained search officers from North Yorkshire Police, experts from the North East Counter Terrorism Unit, explosives detection dogs, the National Police Air Service and military search personnel.
Superintendent Dave Hannan of North Yorkshire Police said: "We are satisfied that the call to the police was made with good intent.
"We appreciate that members of the public will ask why the road had to be shut for so long.
"In view of the location of the suspected explosion, the source of the information, the current threat to UK security and a report a few hours earlier of a vehicle seen in suspicious circumstances outside the barracks, we were not prepared to take any chances with people's safety and had to carry out a very extensive and thorough investigation.
"Officers have worked throughout the night and day to identify and locate the driver of the vehicle and we are now satisfied that he was not connected to the reported explosion and we have now eliminated him from our enquiries.
"We thank the driver of the vehicle for his patience and cooperation. We have also ruled out any link to terrorism."
He thanked members of the public caught up in the congestion, adding: "Their safety was our prime concern."
Supt Hannan said: "We may never find out what the source of the explosion was, however, following the search and investigation I am now satisfied that there is no threat to members of the public.
"A number of possibilities have been looked into, however, there is no information or evidence to say this reported explosion was a criminal or deliberate act."
While the explosion "remains unexplained", police discovered a "box of ageing detonators" during their search of the area.
The army's bomb disposal unit was called to the discovery near the perimeter fence of Marne Barracks.
These have now been removed for safe disposal, but were not the cause of the reported explosion.
There have been no other reports of damage in the area and the police search was ongoing all day to locate any scene of the explosion.
Police said their search has been affected by darkness and poor weather conditions.
In an earlier statement, the force said the search remained "focused on the area outside of the barracks and the area adjacent to the A1, although at this stage, it cannot be ruled out that it has occurred within the boundary of the barracks".
Royal Military Police from the Garrison could be seen in their distinctive red caps assisting police by directing traffic in the village of Catterick and speaking to drivers.
A spokesman for Catterick Garrison said four houses within the garrison but outside the barracks had been evacuated.
Those people were later able to return to the houses, he added.
On the Ministry of Defence (MoD) website, Catterick Garrison is described as the army's "largest training establishment".
It covers 2,400 acres as well as 20,000 acres of training land.
The garrison is situated just a few miles from the A1 and includes Marne Barracks near Catterick Village and the outstations of Ripon, Dishforth and Topcliffe.
Catterick Garrison provides a base for Headquarters 4th Infantry Brigade and Headquarters North East which forms part of 1st (United Kingdom) Division, according to the MoD website.
There are over 13,000 personnel, military, civilian and their dependants, living and working in the area.
Both slip roads to Catterick were also closed, diversions were in place and motorists were advised to avoid the area.
Football fans were expected to be among the motorists affected by the road closure.
Newcastle United said they notified West Ham United officials that travelling supporters would be affected.
The North East football club were playing West Ham United today at the latter's Upton Park ground in east London.