Cannabis plants, believed to be worth millions of pounds, have been seized by police.
Officers attended an industrial unit, in the Burcott Road area of Avonmouth, and discovered the significant quantity of cannabis plants on Monday 17 October.
The estimated street value of the plants is approximately £3.5million.
Enquiries to identify those responsible for the production of a class B drug is ongoing.
Inspector Steve Davey said: “Since the discovery of these cannabis plants work has taken place to remove them and make sure the area is safe.
“A criminal investigation is underway to ascertain who was responsible for this large and seemingly professional illegal operation.
“We would like to take the opportunity to ask the public to report any suspicious activity around industrial units or abandoned businesses that may be being used for criminal activity, such as has been the case in Avonmouth over a significant period of time.”
Anyone with information that could help our investigation is asked to call 101 and give reference number 5222249859.