West Midlands police were looking for a cannabis farm in an industrial unit when they stumbled across the bitcoin mine, according to a police report released Thursday.

Police said there were indications that the unit was being used as a cannabis farm so they initiated the May 18 search of the Great Bridge Industrial Estate in Sandwell. A police drone had detected a considerable amount of heat coming from the building, police said.

Also, people were visiting the industrial unit several times during the day and numerous wiring and ventilation ducts were visible.

No cannabis was found, but police discovered a bank of about 100 computers and the equipment was seized.

The police search found no one at the unit and no arrests have been made. Police said they were searching for the owner of the unit.

"It's certainly not what we were expecting," said Sandwell Police Sgt. Jennifer Griffin in a statement. "It had all the hallmarks of a cannabis cultivation set-up and I believe it's only the second such crypto mine we've encountered in the West Midlands. My understanding is that mining for cryptocurrency is not itself illegal but clearly abstracting electricity from the mains supply to power is."