A 100m cordon was put in place around Memorial Gardens and Queens Way after the item was discovered in a bin.
Police evacuated the town centre at about 6.20pm and closed part of College Road and Southgate Avenue whilst they investigated the incident.
In videos recorded at the scene viewers can hear a large bang which is believed to have been carried out by the bomb disposal unit.
An eyewitness said officers had carried out a 'controlled explosion' in the area.