A three-floor cannabis factory has been discovered in a former nightclub, with the crop said to have a street value of more than £1m.
The National Crime Agency (NCA) said its officers found about 1,000 plants at the Coventry premises, one of the largest hauls it had ever seen.
The growing and irrigation uncovered at the Trinity Street property were described as sophisticated.
Three men have been charged with drugs offences following the NCA's raid.
Officers had to smash through several reinforced doors to access the plants during Thursday's operation at the unnamed city centre site, in which growing equipment valued at about £150,000 was also found.
'Significant and sophisticated'
NCA branch commander Adam Warnock said the seizure of drugs would dent the profit of organised crime which benefited from large-scale drug-growing.
"The size of the cannabis factory was significant and sophisticated, spread across three floors of a large building," he said.
"It is certainly one of the largest grows ever uncovered by the NCA."
Mr Warnock added investigations were continuing.
The NCA said two men, aged 24 and 31, had been charged with production of a class B drug and appeared before magistrates on Friday.
A third man, 28, accused of the same offence, was subject of an extradition hearing, the NCA added.
West Midlands Police assisted with the operation, using drones to help detain two suspects.