Police have seized and destroyed 900 cannabis plants from Nelson and Marlborough in this year's drug operation - and some social media commentators have criticised the haul. (File photo).

Police have hit back at social media trolls who called the seizure of more than 900 cannabis plants a waste of time.

About 30 police officers took part in a Tasman operation to prevent the supply of drugs at the start of March, and posted information of the seizure on the Nelson, Marlborough West Coast Police Facebook page.

Commentators were quick to criticise the operation, with the majority of the comments questioning the purpose of targeting cannabis.

DEREK FLYNN/FAIRFAX NZ Community Constable Russ Smith says social media backlash to a police seizure of cannabis is disappointing.

Community Constable Russ Smith, of Blenheim, said it was very disappointing to read the reaction.

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"The public don't seem to understand the connection between the cultivation of cannabis and these criminal fraternities and other class A drugs," he said.

SUPPLIED Tasman District Commander Superintendent Mike Johnson says cannabis remains an illegal substance and police will continue to enforce the law.

"It is disappointing that people think we are wasting our time."

Removing cannabis and grow operations hit crime rings where it hurt most, their finances, Smith said.

Social media commentary was not always well-informed and many of the comments fed into other negative posts, Smith said.

"The public don't see what we do. They don't understand that there is a very strong connection between people who grow it commercially and the criminal world," he said.

Of the 40 or so comments, Smith said he noticed only two were positive towards police and the cannabis seizure.

"We don't dwell on this. It doesn't make us want to quit our jobs or anything," he said.

Police said on Monday they had seized and destroyed 900 cannabis plants from Nelson and Marlborough in this year's drug operation.

The drug sting reported a 75 per cent drop in cannabis plant seizures following a police decision not to use helicopters.

A total of 6000 plants were seized in the top of the South last year.

Tasman District Commander Superintendent Mike Johnson said he understood that cannabis was a divisive issue, but it remained an illegal substance.

"It's an emotive topic for a lot of people, and it is public debate," he said.

"But we're not charged to comment on these issues, we're here to enforce the law of the land.

"I know there is a lot of polarisation of feeling around cannabis in the political arena but there is a law which makes it illegal. And we certainly won't step aside in enforcing the law."