A paintball gun in a parcel triggered a bomb alert which brought Diss town centre to a standstill for three hours with the evacuation of hundreds of shop staff and pedestrians from the high street.

Police and Explosive Ordnance Disposal officers were called after the suspicious package was found at a Royal Mail delivery office in Diss Market Place at 9.30am on Tuesday.

A 200m exclusion zone was set up around the office and Market Place and Mere Street were closed, with police herding staff and shoppers behind police tape set up across Mere Street at the junction with Chapel Street opposite the tourist information centre.

However, a police spokesman confirmed the package proved to be a genuine parcel – a paintball gun – and the cordon was lifted after three hours.

Jason Beeton, manager of the Boots store in Market Place, said a customer had said the Post Office had been closed because of a suspected bomb, but he did not pay too much attention to it until he heard something official from the police.

However, when he saw the road being closed off outside he approached one of the officers who told him there had been a 'credible threat' and he would need to evacuate the building.

He said: 'The evacuation was relatively straightforward. There were a lot of people that were perhaps a bit confused, but otherwise it was all fairly orderly. The police did not give us any details of what it was, just that it was a credible threat and we needed to get a safe distance away.'

Another evacuee David Bracegirdle, manager of Carphone Warehouse, said: 'There was no great panic, really – people were just ambling away from the scene.'

Royal Mail spokesman Sally Hopkins said: 'We can confirm that a suspect item was found in Diss delivery office and on the advice of the police the building was evacuated and an exclusion zone was set up around the site.

'There was no disruption to deliveries.'