Thousands of tractor-driving Dutch farmers stepped up protests on Wednesday against the government's climate policies, prompting authorities to block off parliament with army vehicles.

In the second national demonstration in three weeks against government plans to curb nitrogen emissions, farmers laid siege to the country's seat of power in The Hague, causing widespread travel disruption.

The Dutch farmers' action caused widespread disruption to road users
The Dutch farmers' action caused widespread disruption to road users ANP / Robin van Lonkhuijsen

Honking their horns, the farmers drove from cities across the country and parked their tractors on a central park a few blocks from parliament, which was blocked off by police and the military.

"We've been angry for a long time," small-scale farmer Rik Oosterveld told AFP to the sound of hooting and fire crackers going off.

The farmers are protesting at new restrictions on nitrogen emissions, which they say will hit their industry hard
The farmers are protesting at new restrictions on nitrogen emissions, which they say will hit their industry hard ANP / Remko de Waal

"It's been one rule after the other against farmers, and now it's nitrogen. We're done with it."

Farmers listened to speeches and music, while police in riot gear kept a close eye, a water cannon stood on stand-by, and a military helicopter circled overhead.

A similar protest on October 1 caused the Netherlands' biggest ever traffic jam.
A similar protest on October 1 caused the Netherlands' biggest ever traffic jam. ANP / Jerry Lampen

The tractor protest caused 450 kilometres (280 miles) of traffic, especially around the central city of Utrecht, the ANWB traffic agency said.

Public transport was also halted in the centre of The Hague after a breakaway group of farmers in tractors escaped the police cordon and occupied a main square.

A similar protest on October 1 caused the Netherlands' biggest ever traffic jam.

Security was tightened for Wednesday's main protest after trouble during a provincial protests in the northern city of Groningen on Monday when a tractor barged through the doors of the provincial administration building.

Both Prime Minister Mark Rutte's ruling VVD party and one of its three coalition partners, the Christian Democrats, have voiced doubt about nitrogen figures in the country given by the National Institute for Public Health and the Environment (RIVM).

The institute fingered the Dutch agricultural sector as the largest producer of nitrogen, saying it produced a total of 106 million kilogrammes of the gas in 2017.

Some 94 million kilogrammes came from stock breeding, the RIVM said.