Thieves forced open the door of an abandoned house and then removed stones in a dividing wall to reach into the Sterling Jewellers outlet in Mellieħa on Wednesday night.
The value of the stolen items was not disclosed and it is understood the thieves may have grabbed whatever they could reach from the hole.
The police said they were informed of the theft at 9.40 a.m. by a salesman who opened the shop and did not immediately realise it had been burgled. He thought a wall had collapsed. The alarm of the outlet, situated in Borg Olivier Street, for some reason did not go off. The area around the shop is monitored by CCTV cameras.
Earlier this year, two other outlets belonging to Sterling Jewellers, one in Sliema and the other in St Julians, were robbed during hold ups.