Two cyclones that hit the top of the South Island and West Coast in February did not appear to dent the annual cannabis haul, police say.

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Just over 7000 plants have been destroyed after they were seized in the Tasman region operation, which covers Nelson, Marlborough and the West Coast, Tasman District operations manager Inspector Dan Mattison said.

The annual operation recovered 3789 plants in Nelson/Marlborough and 3283 on the West Coast.

It was carried out during and after the storms, but police said there was not widespread damage to crops found on public and private land.

Mr Mattison said the most successful warrant led to the seizure of 500 plants at Stillwater, near Greymouth, along with 1.3kg of head/leaf material. Two firearms were also seized.

He said the total amount of cannabis plant seized was similar to last year. Seven people were apprehended, four of whom face charges around cultivation of cannabis.

The national operation runs for several months and includes search warrants and targeted enforcement relating to other drugs, organised crime and proceeds of crime.