Armed police officers were mobilised following a 999 call reporting a sniper firing a shot through the open window of a borough council building in Yarmouth.

Armed police officers were mobilised following a 999 call reporting a sniper firing a shot through the open window of a borough council building in Yarmouth.

Staff in Greyfriars House and the nearby Town Hall were warned by police control to close all windows, stay inside and keep doors shut until officers could get there.

It was only when police had checked a first-floor office in Greyfriars House, in Greyfriars Way, and identified a round on the floor as the plastic pellet of a BB gun that the incident was down-scaled and an armed police unit taken off standby.

A 20-year-old man was later arrested at a nearby property and interviewed before being given a formal police caution for causing criminal damage.

Simon Baker, the council's housing support services manager, raised the alarm at about 4.30pm yesterday after he was startled by the noise of the shot.

He said: 'I was working at my desk with the window open when the round came in and ricocheted around the walls before it landed on the floor.

'When I rang the police, we were advised to stay inside the building and not let anyone in until officers got there. Council staff were obviously anxious to be told there was an ongoing security incident but it was all over in about 15 minutes.

'Although it only turned out to be a BB gun, the pellet would have certainly caused serious damage if it had hit someone in the eye.'

Insp Nick Russell, who co-ordinated the operation, said: 'When the call first came in we treated it very seriously and officers with firearms were put on standby.

'People inside the building were very shocked although officers were quickly able to identify the pellet from a BB gun and ascertain there was no risk to life.'

He said police managed to identify the premises from where the shot had come and arrested the culprit.

Council managers were today considering the incident to see if any changes needed to be made to their security arrangements.