Police, Fire and specialist EOD officers from the Royal logistics corps have all been scrambled to Tesco at Quay Street in the town this lunchtime.
Emergency service were called at around 1pm on Thursday following the discovery of a suspect package. The store has been evacuated and safety cordons have been put in place.
A number of officers from Hampshire Police and firefighters from Hampshire and Isle of Wight fire and rescue remain at the scene.
It’s not clear if the device is a viable threat.
Hampshire Constabulary have been approached for comment and are expected to issue a statement shortly.
Specialists EOD officers have also been called to carry out an inspection using an x-ray machine.