About 500 French riot police swooped on anti-airport demonstrators in an early-morning raid.
Gendarmes fired teargas and scuffled with some of the hundreds of protesters who have been occupying the area earmarked for the new Notre-Dame-des-Landes airport, near the city of Nantes in western France, for a week.
"The most radical opponents are resolute [in carrying] on guerrilla [tactics] to stop work at the airport," a spokesperson for the French Interior Minister told Le Figaro.
"We were taken by surprise, but many protesters are still [hiding] in the trees," an occupier who gave his name only as Jerome said.
Between 13,000 and 40,000 people have been demonstrating against the new €580 (£470) airport project.
Opposition to the construction of Notre-Dame-des-Landes, planned to replace Nantes-Atlantique airport, dates back to the 1970s when the project was first mooted. It has been formented by environmentalists and farmers, whose land has been expropriated to make way for construction.
It was not until 2008 when the green light was given. Work is due to be completed by 2017.
Some farmers went on a 28-day hunger strike against eviction earlier in 2012, leading to a temporary suspension of works by construction companies.