A global figure in the fight against climate change, Thunberg has been fined by one Swedish court for her direct action protests there. But she saw another case against her thrown out by an English court last week.

Wearing a Palestinian scarf and an anorak, Thunberg joined other protesters under heavy rain at the site in Saix where a new motorway – the A69 linking the southwestern city of Toulouse to the town of Castres – is planned, AFP journalists saw.

They held up banners saying “Stop A69”. Critics of the project say it is harmful to the environment and does not take into account the current climate crisis.

The protest organisers had gone ahead with the rally despite authorities banning the gathering because of “risks of serious harm to public order”.

AFP journalists saw at least two arrests and the use of tear gas by police at the site yesterday.

Activists had set up camp toilets and signposts on private land where they planned to create a so-called “zone to be defended”.

Police cleared pallets and trolleys used to block a small road running alongside the field, which is close to the route of the planned motorway.

A police source told AFP they expect up to 200 people to attend the protest, while organisers estimated between 500 and 1,000.

“We’re going ahead with the event because it’s a private event on private land,” said Paul, a spokesman for the movement who asked not to give his family name.

He added that the wooded area is the subject of a dispute over its expropriation for the motorway. Local authorities say the land is illegally occupied.

Environmentalists have protested several times in recent months along the planned route of the A69.