Police have seized more than 2000 cannabis plants, drugs utensils, and illegal firearms in a series of search warrants in the South Island.

About 30 staff took part in an operation, which started two weeks ago, Inspector Dan Mattison said.

In the Nelson and Marlborough areas, about 900 cannabis plants were recovered.

Police also seized two illegal firearms, one of which was loaded, $1700 in cash, and meth and cannabis utensils.

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Police executed 12 search warrants, six at residential addresses and a further six at rural locations.

One indoor growing system was found.

Separately, police visited about 50 sites on public land.

Seven people will be prosecuted, and one person received a warning.

On the West Coast, almost 1300 cannabis plants were recovered.

Ten firearms were recovered from a licensed firearms holder, and police will examine whether the licence should be revoked.

At one public plot, more than 400 plants were recovered.

"The supply of illicit drugs has a big impact on our community," Mattison said.

People are committing dishonesty crimes such as burglary to fund their habit.

"We will ensure that anyone involved in drugs is referred to the appropriate agency for help.

"I also urge anybody that has a drug or alcohol addiction to contact the Alcohol Drug Helpline on 0800 787 797."

All of the plants have been destroyed.