Cannabis plants with an estimated street value of £3.5m have been seized by police in Bristol.
Officers discovered a cannabis factory inside an industrial unit near Burcott Road in Avonmouth on 17 October.
Insp Steve Davey said: "A criminal investigation is underway to ascertain who was responsible for this large and seemingly professional illegal operation."
Anyone with information is asked to contact Avon and Somerset Constabulary.
Enquiries to identify those responsible are ongoing
"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," added Mr Davey.