The property, which was previously known as Beavis, is currently being renovated and was accessed via a boarded up window in Chapel Street.
Once inside, thieves have stolen two Makita drills, along with their batteries and a charger and a red Carrera mountain bike.
It is believed the suspects left the building via a side door on to Chapel Street.
A spokesperson for Hampshire Constabulary said:
“We’d like to hear from anyone who witnessed anything suspicious in the area, or has been offered these items for sale”.
Anyone with information is asked to call 101 on 44160490327 or call the Crimestoppers charity anonymously on 0800 555 111.