A fire broke out at a disused boxing club just days after police found a cannabis farm growing inside.
Fire crews battled for nearly an hour to put out the blaze at the Edward Street building in Morecambe town centre on Tuesday afternoon.
A crowd gathered to watch as flames and smoke billowed from the premises where police had discovered up to 1,000 cannabis plants a few days before.
The fire caused “substantial damage” and smoke lagging to the room where it began.
Emergency services got the call at around 3.25pm on Tuesday and three fire engines raced to the scene.
An investigation is under way as to how the blaze started.
Spokesmen for Lancashire police and Lancaster fire station were unable to confirm if the fire began in a room where cannabis had been found.
Lancaster City Council has been asked to board up the building.
Police discovered the cannabis factory set up over five rooms on two floors after raiding the premises last Thursday.
The building was cordoned off until Sunday as CSI officers scoured the building and the plants, which had an estimated street value of half a million pounds, were removed and destroyed.
Police also found sophisticated hydrophonic equipment and that the electricity supply had been re-routed to help cultivate the plants.
An organised criminal gang is thought to be responsible for the cannabis farm.
Anyone with information about the cannabis factory should contact police on 101 or freephone Crimestoppers on 0800 555111 where callers can remain anonymous.