Part of Great Harwood town centre has had to be closed off after cracks were discovered in the town hall’s frontage.
Market-goers are now being warned to keep away from the building.
A section of the road has been closed as a precaution by Lancashire County Council, as well as a pedestrian area cordoned off.
The rest of Town Hall Square will be unaffected so it is not expected to affect the running of the market.
The cracks were discovered as builders began work on a £500,000 refurbishment to turn the historic hall into a centre for small businesses.
The Victorian listed building, which has been out of use since the dissolution of the urban district council in 1974, was sold to Globe Enterprises earlier this year, for a figure believed to be in the region of £375,000.
Work is now underway to turn it into a "business and enterprise hub" for start- up firms.
Deputy leader of Hyndburn council, and the man in charge of the redevelopment, Councillor Peter Clarke said: "This is a bit of a setback but not a disaster.
"The building’s been there doing nothing for 36 years but looking at it now it was an accident waiting to happen.
"It’s just good we’ve discovered these cracks now and can get to work straight away to rectify them."
The deep cracks were discovered whilst the builders were putting up scaffolding and carrying out work on the inside of the hall.
It is not yet known what the additional cost to the project will be.
Both Coun Clarke and Globe Enterprises are hopeful the repairs can be completed by the end of January and the opening date set for around March won’t have to be pushed back.