Cannabis plants worth around £800,000 have been found in a disused building in Halifax after properties nearby reported power cuts.
Calderdale police officers were called out to Portland Place by engineers after suspicions were raised regarding the former office block.
More than 600 cannabis plants were found at the sophisticated production plant which spanned five floors.
The factory has now been dismantled and the equipment and plants seized.
Sgt Joshua Allgood of Halifax Neighbourhood Policing Team, said: "We will continue our relentless disruption tactics and keep working to take drugs off the streets of Halifax.
"Our enquiries remain ongoing to bring those responsible for this production to justice."In the meantime, please report any information you have about drugs supply to us or anonymously via Crimestoppers."