Four Greenpeace activists have been arrested after shutting down a coalmine used to help power a Fonterra dairy factory.

Inspector Olaf Jensen said up to 12 protesters were involved.

He said four people were arrested and charged with trespassing shortly after 6.30am.

Mr Jensen said the activists had chained themselves to equipment and blocked the entrance but given the "swift response" from police the coal mine was back up and running.

"There was no real interruption to the coal mine," Mr Jensen said.

The activists had unfurled a 40sqm banner reading "Fonterra Climate Crime" at the New Vale mine, near Gore in Southland.

Greenpeace said lignite coal was one of the "dirtiest fossil fuels" and Fonterra's use of it to power milk dehydrators at its Edendale milk processing plant was a "climate crime".

Fonterra's general manager of sustainable production, John Hutchings, said the Greenpeace protest had not had any immediate impact on dairy processing at the Edendale plant.

He said Fonterra used the best mix of "a range of energy sources - including coal at some sites" and was constantly searching to improve energy efficiency.

Mr Hutchings said Fonterra had to be internationally competitive, which required being being energy efficient.

Improvements in processes since 1990 meant Fonterra now produced 300,000 less tonnes of C02 per annum, he said.

However, Greenpeace said Edendale's annual carbon emissions from the use of lignite coal was the equivalent of emissions from more than 87,000 cars.

Spokesman Simon Boxer said Fonterra was putting profit before the climate and the Government needed to bring it "under control".

"By being exempt from the Emissions Trading Scheme (ETS), until 2015, agricultural greenhouse gas emitters are currently receiving a $1.1 billion subsidy from taxpayers," he said.

"This is a direct subsidy that will allow Fonterra to continue to increase its greenhouse gas emissions at the expense of the taxpayer.