A jewellers was targeted by thieves who cut a hole in the roof and lowered themselves into a market stall.
Police believe the brazen thieves measured the top of the Fleetwood Market business before cutting out a section, causing £5,000 damage.
The men attempted to access the safe once they were inside the building but did not leave with any money following the raid, which police believe happened sometime between 4.30pm on Saturday, 23 and 8.30am on Tuesday, 26, November.
Det Con Emma Shuttleworth, of Fleetwood CID, said: “It is clear there has been a large amount of planning that has gone into this burglary.
“The thieves have maliciously measured the roof so they have dropped right into the stall.
“I appeal to anyone who has CCTV in operation in an around the market in Adelaide Street to check it for anything suspicious.
“I also appeal for anyone who saw people on the roof of the market while it was closed Sunday and Monday to come forward and contact police.”
Josephine Mayer, owner of Jade Jewellers, said: “I was devastated when I heard what had happened.
“The girls opened the doors to get into work on Tuesday and the roof was missing.
“We’ve had to close off the stall because there’s a lot of damage but nothing was taken and the safe did its job.
“This could’ve ruined my business and I’m delighted nothing was taken.”
Mrs Mayer’s other shop, on Lord Street, is still open for business.
Call (01253) 604306.