Two men broke into Station Jewellers on Merkland Street in Glasgow's Partick area and snatched diamond rings, necklaces and watches.
The items, taken between 2am and 5am today, have been valued at six figures.
Police believe a third man may have helped the pair flee the scene.
Detective Constable David Hardie said: "We know from the CCTV that there were at least two men - both white, wearing dark clothing and carrying plastic carrier bags - involved.
"They ran from the back of the shop and into the rear lane then into Dumbarton Road. It is possible that there was a third man waiting in a car for them but that has not been fully confirmed as yet.
"Flats overlook the shop and the rear lane so it is very possible that someone may have heard noises coming from the shop or maybe a car with its engine running for an excessive period of time.
"I would appeal to anyone who was in the Merkland Street area, where the taxi rank and train station is, who may have seen or heard anything suspicious, or indeed who may have information about the break-in to contact police.
"Information can be passed to officers at Partick police office via the non emergency number 101 or in confidence to Crimestoppers on 0800 555 111."