Firefighters discovered a cannabis factory at a property in Salisbury Road, Worthing, last night while they searched for people trapped in a house fire.
Crews were called to the house at about 8.30pm after a report of a fire and that there could still be residents inside the home.
There was no one inside the flat on fire but a cannabis factory was found set up on the top floor.
Two residents of the ground floor flat were present and were alerted by a neighbour across the street that their drainpipe was on fire.
They evacuated the building.
Detective Sergeant Colin O’Hare, of West Sussex CID, said: “The home was split into several flats and the top floor flat had been turned into a cannabis factory with hydroponics equipment.
“We’d like to speak to anyone who has any information who may have noticed witnessed anything of relevance or an unusual smell coming from the building.
“We would also like to know about who has been visiting the address over the last few weeks and months and hope residents can help us.
“Please contact us if you have any information at all.”
Crews left the premises at 10.30pm.
Anyone with information should call 101 quoting serial 1414 of 11/12, email firstname.lastname@example.org or call the independent charity Crimestoppers anonymously on 0800 555111.