New Zealand on Tuesday unveiled plans to tax the greenhouse gas emissions from farm animals, in a controversial proposal designed to tackle climate change.

Prime Minister Jacinda Ardern said the levy would be the first of its kind in the world.

Gases naturally emitted by New Zealand's 6.2 million cows are among the country's biggest environmental problems.

The scheme would see farmers pay for gas emissions from their animals, such as methane gas in the farts and burps from cows, and nitrous oxide in the urine of livestock.

Ardern told farmers they should be able to recoup the cost by charging more for climate-friendly products.

She said the "pragmatic proposal" would reduce agricultural emissions while making produce more sustainable by enhancing New Zealand's "export brand".

The government hopes to sign off the proposal by next year and the tax could be introduced in just three years' time.

But with New Zealand going to the polls in the next 15 months, the proposal could cost Ardern rural votes as farmers quickly condemned the plan.

Andrew Hoggard, president of the Federated Farmers lobby group, said the scheme would "rip the guts out of small-town New Zealand".

He argued the tax could push farmers into growing trees on fields currently used to rear livestock.

Beef + Lamb New Zealand, representing the country's sheep and cattle farmers, said the plan failed to take into account rural measures already in place to counter greenhouse gases.

"New Zealand farmers have more than 1.4 million hectares of native forest on their land which is absorbing carbon," said chairman Andrew Morrison.

"It's only fair this is appropriately recognized in any framework from day one."