Police have uncovered a hydroponic hotbed of cannabis plantations in the Sydney suburb of Mascot, in a seizure worth more than $2 million.

The marijuana manufacturing operation, in an industrial complex on Chalmers Crescent, was powered by an extraordinary web of plug boards and extension leads connected to dozens of mains switches.

Police found a web of plug boards and extension leads. Credit:NSW Police Media Unit

"It was an extremely large hydroponic set-up," said Detective Chief Inspector Stuart Bell, who led the Redfern Region Enforcement Squad raid.

"They'd obviously spent a lot of time and money setting up."