The plants, which detectives claim are worth at least pounds 1m, were being grown in a make-shift greenhouse under plastic sheeting and dozens of fluorescent strip lights inside a derelict warehouse.
Four men were arrested in Manchester after the operation recovered what police believe to be the largest amount of the drug ever found growing in the UK.
The drug, known as "skunk" because of its pungent smell, is much more powerful than normal cannabis and each plant is worth about pounds 1,000.
Also known as "super skunk", most of it is smuggled in from the Netherlands although increasingly it is being grown in Britain. There is a growing demand for the drug because of its potency, a fact identified by dealers who have increased their supplies in recent years.
At about pounds 15 for a sixteenth of an ounce (1.75 grams) - about enough for three very strong cigarettes - it is twice as expensive as normal cannabis.