Most of the country is sweltering under a summer heatwave compounded by a record drought -- conditions most experts say will occur more often as a result of rapid climate change. 

"We must continue, more than ever, our fight against climate disruption and... adapt to this climate disruption,"

Prime Minister Elisabeth Borne said after arriving at a fire-command post in the village of Hostens, south of Bordeaux.

The European Commission said four firefighting planes would be sent to France from Greece and Sweden, as well as teams from Austria, Germany, Poland and Romania.

"Our partners are coming to France's aid against the fires. Thank you to them. European solidarity is at work!" President Emmanuel Macron tweeted.

"Across the country over 10,000 firefighters and security forces are mobilized against the flames... These soldiers of fire are our heroes," he said.

In total, 361 foreign firefighters were dispatched to assist their 1,100 French colleagues deployed in the worst-hit part of the French southwest.

A first contingent of 65 German firefighters, followed by their 24 vehicles, arrived on Thursday afternoon and were to go into action at dawn on Friday, officials said.

Among eight major fires currently raging, the biggest is the Landiras fire in the southwest Gironde department, whose forests and beaches draw huge tourist crowds each summer.

It had already burned 14,000 hectares (35,000 acres) in July -- the driest month seen in France since 1961 -- before being contained, but it continued to smolder in the region's tinder-dry pine forests and peat-rich soil.

Since flaring up again on Tuesday, which officials suspect may have been caused by arson, it has burned 7,400 hectares, destroyed or damaged 17 homes and forced 10,000 people to quit their homes, said Lieutenant Colonel Arnaud Mendousse of the Gironde fire-and-rescue service.

Borne said nine firefighting planes are already dumping water on the blaze, with two more to be in service by the weekend.

"We battled all night to stop the fire from spreading, notably to defend the village of Belin-Beliet," Mendousse told journalists in Hostens.

On several houses nearby, people hung out white sheets saying: "Thank you for saving our homes" and other messages of support for the weary fire battalions.

"You'd think we're in California, it's gigantic... And they're used to forest fires here but we're being overwhelmed on all sides -- nobody could have expected this," Remy Lahlay, a firefighter deployed near Hostens in the Landes de Gascogne natural park, said.

With temperatures in the region hitting nearly 40 degrees Celsius on Thursday and forecast to stay high until at least Sunday, "there is a very serious risk of new outbreaks" for the Landiras fire, the prefecture of the Gironde department said.

Acrid smoke has spread across much of the southwestern Atlantic coast and its beaches that draw huge crowds of tourists each summer, with the regional ARS health agency "strongly" urging people to wear protective face masks.

The smoke also forced the closing of the A63 motorway, a major artery toward Spain, between Bordeaux and Bayonne.

The government has urged employers to allow leaves of absence for volunteer firefighters to help fight the fires.

In Portugal on Thursday, more than 1,500 firefighters were also battling a fire that has raged for days in the mountainous Serra da Estrela natural park in the center of the country.  

It has already burned 10,000 hectares, according to the European Forest Fire Information System (EFFIS).