Hundreds of cannabis plants were found when police raided premises in Thorne, Doncaster, yesterday.
The existence of the drugs factory was discovered after a fire was reported at a shop in South Parade about 9.30am.
When firefighters checked the flats above they found the production unit.
A police spokesman said a total of 250 cannabis plants were discovered and the road was closed for nearly two hours while officers removed them.
The flat was not occupied at the time of the incident and investigations showed the electricity supply meter had been bypassed.