More than 2,000 cannabis plants worth about £300,000 have been seized in Bradford city centre, police said.
Officers visited an address in Morley Street at about 10:00 BST on Thursday amid concerns over hazardous materials, and discovered a cannabis farm.
The plants were seized and a cordon put in place. West Yorkshire Police said an investigation was under way to find out who used the building.
Police have appealed for anyone with information to get in touch.