Thousands of farmers have gathered in the Netherlands to protest the Dutch government's plans to rein in emissions of nitrogen oxide and ammonia, driving their tractors across the country and snarling traffic on major highways.
The protest was organised earlier this month after the government published targets for reducing emissions, sparking anger from farmers who claim their livelihoods - and those of thousands of people who work in the agricultural service industry - are on the line.
Calling it an "unavoidable transition," the government mandated reductions in emissions of up to 70 per cent in many places close to protected nature areas and as high as 95 per cent in other places.
The government has been forced to act after courts in recent years began blocking permits for infrastructure and housing projects because the country was missing its emissions targets.
Organisers said 40,000 farmers converged on a green field in the small agricultural village of Stroe, about 70km east of the capital Amsterdam.
A stage was set up for speakers to address the crowd and music blared out of speakers while children bounced in a giant inflatable pig.
Farmers hooted their tractors' horns as they drove onto the field, where a banner on a truck read, in Dutch, "What The Hague chooses is deeply sad for the farmer," a reference to politicians in the city that houses the Netherlands' parliament.
Another banner on a tractor said: "We can no longer be stopped."
Marijan van Heun, a 23-year-old dairy farmer from the central Utrecht province, said the government plans were stripping young farmers of their futures.
"We cannot invest. Our fathers, our uncles, cannot invest in the future. And so as young farmers we also have no prospect of... taking over a farm," he said.
The Dutch infrastructure authority urged motorists to delay travel as slow-moving convoys of tractors defied appeals not to use highways as they drove toward the demonstration.
Authorities warned later that roads, particularly around the demonstration, would remain clogged into the evening as farmers drove home.
One of the country's busiest highways was completely blocked by tractors.
Earlier, in The Hague, a few dozen farmers and their supporters, some wearing T-shirts with the text "No farmers, no food," gathered for a breakfast before heading to the protest.
"This is where the rules are made," said dairy farmer Jaap Zegwaard, who parked his tractor on the edge of a park in the city.
"I was asked to come here and provide breakfast so we can show we are food producers, not pollution producers."
The ruling coalition has earmarked an extra 24.3 billion euros ($A37.0 billion) to finance changes that will likely make many farmers drastically reduce their number of livestock or to get rid of them altogether.
The plans, which have to be carried out by provincial governments, have been opposed even by members of Prime Minister Mark Rutte's own party and other members of his coalition.
Provincial governments have been given a year to formulate plans to meet the reduction targets.
One government lawmaker, Tjeerd de Groot, tweeted that he had planned to attend to discuss the plan with farmers but called off his trip on the advice of a government security agency.
"Does the law of the tractor apply in our country?" he tweeted.
Farming is a key sector in the Dutch economy, with exports worth nearly 105 billion euros last year.
Zegwaard said farmers were prepared to talk about how to reduce emissions but objected to the industry shouldering most of the blame.
"Now the agricultural sector is dismissed as a major polluter and that is not right," he said.
Australian Associated Press
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