A security cordon was thrown around RAF Kinloss after the incident near the front gate of the Moray base.

The Ministry of Defence (MoD) said base staff had been advised not to turn up for work and the general public was being warned to stay away.

The MoD said the incident at the closure-threatened base, where 3,000 personnel work, was not related to terrorism or any protest.

Grampian Police confirmed they were searching the RAF base for a 40-year-old serviceman who is believed to have a firearm in his possession.

The specially-trained officers were being assisted by a helicopter from RAF Lossiemouth.

Police described the wanted man as white, 6ft 3in and of medium build, with short cropped hair and a moustache. He is wearing black jogging trousers, a red anorak and a red woolly hat.

Chief Inspector Alan Smith said: "Our primary concern is public safety. Although we have no specific intelligence that this man is a threat to the public, we must use due caution.

"I would urge the public to assist us and to avoid the RAF Kinloss area at the moment. I would also urge anyone living nearby to remain indoors. As soon as the situation has been resolved I will make the public aware through the media.

"If anyone sees a man matching his description they should not approach him and should contact Grampian Police on 999 immediately."