Farmers said their objective was to establish eight chokepoints on major roads into Paris.
“We need answers,” said Karine Duc, a farmer in the southwestern Lot-et-Garonne department, as she joined a convoy of tractors heading for Paris.
“This is the final battle for farming. It’s a question of survival,” she said.
A banner on a tractor in the convoy said: “We will not die in silence.”
In response, the government ordered the deployment of 15,000 police and gendarmes.
Interior Minister Gerald Darmanin told security forces to show restraint. But he also warned the farmers not to interfere with strategic spots.
German farmers drive tractors into Berlin to protest fuel subsidy cut
German farmers drive tractors into Berlin to protest fuel subsidy cut
“We’re not going to allow government buildings or tax offices or supermarkets to be damaged or lorries transporting foreign produce to be stopped. Obviously, that is unacceptable,” he said.
Darmanin said the protests also not be allowed to affect Paris’s Charles de Gaulle and Orly airports, or the Rungis international wholesale food market south of the city.
Armoured police vehicles were deployed to Rungis on Monday after some farmers threatened to “occupy” it.
Police and gendarmes are also under orders to prevent any incursion into Paris itself, said Darmanin.
The government has been trying to keep discontent among farmers from spreading ahead of European Parliament elections in June, which are seen as a key test for President Emmanuel Macron’s government.
Macron called a meeting with several ministers Monday afternoon to discuss the situation, his office said.
During a visit to a farm on Sunday, Prime Minister Gabriel Attal sought again to address farmers’ concerns, after a raft of concessions announced on Friday failed to defuse the crisis.
“I want us to clarify things and see what extra measures we can take,” he said.
Our goal is not to annoy French people or make their lives difficult, but to put pressure on the government
Arnaud Rousseau, leader of the FNSEA main farmers’ union, said he expected to meet Attal later on Monday.
“Our goal is not to annoy French people or make their lives difficult, but to put pressure on the government,” he told the RTL broadcaster.
Earlier, around 30 activists from environmental group Greenpeace launched smoke grenades on Paris’s Place de la Concorde near the Champs-Elysees.
They unfurled a banner in support of the farmers before being escorted away by police.
Taxi drivers staged their own protest movement on Monday against what they say is insufficient pay for the transport of patients by the French health services.
Their go-slows added to the disruption on motorways.
In neighbouring Belgium, farmers have stepped up their own campaign, blocking a key motorway on Sunday as they too demand better conditions.
Dozens of tractors drove at a crawl through an interchange, halting traffic on the E42 motorway just north of Namur in the south of the country.
Farmers protesting outside a Belgian football stadium delayed a weekend match between Racing Genk and Sint-Truiden by 30 minutes.
In recent weeks, farmers’ protests have grown in Germany, Poland, Romania and the Netherlands.