Bomb squad on the scene in Butler Street Pic: Tony Worrall
The Fishergate Shopping Centre has been closed since 9am on Thursday after a suspicious device went off in a bin.
Preston Police have placed an exclusion zone around the centre, including Butler Street where the Army have positioned a bomb squad.
Police confirmed a device had gone off but had not caused damage or injury in the centre.
Update: The device exploded in a toilet after being found by member of the public
Access to Fishergate car park and the railway station car park is currently restricted, with shoppers being diverted around to Chapel Street to access their cars.
Butler Street is closed to traffic and to pedestrians.