Demonstrators opposed to the airport have erected barricades, occupied cabins and encircled a boggy protected area with 30 tractors in a bid to keep law enforcement officials at bay, according to a report from the France-Ouest newspaper.
One of the barricades was on fire on Monday morning, the newspaper said.
Law enforcement officials were standing back and not intervening.
Police clashed with opponents of the airport on Friday and Saturday after they squatted on the rural land, 30 kilometres northwest of Nantes.
Riot police fired tear gas and squatters threw stones and glass bottles as several thousand people demonstrated in Notre-Dame-des-Landes, AFP reported.
At least seven people were injured in clashes on Saturday.
There have also been demonstrations in the city of Nantes.
The Hollande government wants to clear the 4,000 acres of swampland for a new airport in a project that is straining ties between the ruling Socialists and their Green party allies.
The organizing group of opponents, ACIP, was planning to hold a press conference to outline its aims on Monday.
Cabinet ministers in charge of agriculture, ecology and transport have issued a joint statement in support of the need for the new airport .
Prime Minister Jean-Marc Ayrault’s office has promised to set up a dialogue committee to hear feedback from all sides of the issue.
Ayrault, former long-time mayor of Nantes, supports the new airport, which was initially approved by the previous UMP government after being discussed for more than 30 years.
One of the touted advantages of the two-runway airport, budgeted at more than €600 million, is that it will reduce low-level flying over the city of Nantes, thus reducing noise pollution.
The current airport cannot be expanded because it is too close to the city.