A spate of wildfires is scorching parts of Europe, with firefighters battling blazes in Portugal, Spain, Croatia and southern France amid an unusual heat wave that authorities are linking to climate change.

Hundreds of firefighters, supported by six water-bomber aircraft, were battling on Thursday to bring under control two wildfires in southwestern France that have already burnt almost 4,000 hectares.

"The fires are still not under control, no casualties were reported" said the local authority for the Gironde department, where the blazes, which started on Tuesday, were raging.

The biggest of the two Gironde fires is around the town of Landiras, south of Bordeaux, where roads have been closed and 500 residents evacuated, with the blaze having already burnt 2,100 hectares (5,190 acres).

France, already hit by a series of wildfires over the last few weeks, is suffering - like the rest of Europe - from a second heatwave in as many months.

"Since the start of the year, 15,000 hectares have been burnt in the country, versus a little less than 1,000 hectares at the same date last year ... nine fires out of 10 have a human cause," Interior minister Gerald Darmanin told reporters on Wednesday night.

Elsewhere in Europe, thousands of firefighters battled more than 20 blazes that raged across Portugal and western Spain on Wednesday, menacing villages and disrupting tourists' holidays amid a heat wave that pushed temperatures above 45 degrees Celsius (113 degrees Fahrenheit) in some parts of Europe.

The other one is along the Atlantic Coast, close to the iconic "Dune du Pilat" - the tallest sand dune in Europe - located in the Arcachon Bay area, above which heavy clouds of dark smoke were seen rising in the sky.

That fire has already burnt 1,750 hectares and led to the preventive evacuation on Wednesday of 6,000 people from five surrounding campsites. Another 60 people were evacuated early on Thursday.

In Santiago de Guarda in the central Portuguese district of Leiria, Albertina Francisco struggled to hold back tears as a cloud of black smoke billowed over the tiny village.

Some villagers rescued pets while others helped firefighters battle the flames.

In Leiria, where over 3,000 hectares (7413 acres) have burned so far, authorities blocked major motorways and side streets as strong winds made it harder for firefighters to fight the flames. Portugal's most important highway, connecting its capital Lisbon to Porto, was also blocked due to another fire farther north.

Nearly 900 firefighters were combating three active blazes in Leiria alone, while in the whole of mainland Portugal there were 2,841 firefighters on the ground and 860 vehicles.

In Portugal's southern Algarve region, popular with tourists, a fire broke out in the city of Faro and spread to the Quinta do Lago luxury resort. Videos shared online showed flames edging close to villas, burning palm trees and parts of golf courses.

About half of drought-hit Portugal will remain on red alert for extreme heat conditions on Thursday, with the highest temperatures expected in the Santarem and Castelo Branco districts, the IPMA weather institute said.

Wednesday's highest temperature was registered in the central town of Lousa at 46.3 degrees Celsius (115 degrees Fahrenheit), 1 degree below a 2003 record.

At least 135 people have suffered mainly minor injuries since wildfires began in Portugal last week, and about 800 people have been evacuated from their homes, according to the Civil Protection Authority.

The World Meteorological Organisation warned on Tuesday the heat wave was spreading and intensifying in large parts of Europe.

With human-caused climate change triggering droughts, the number of extreme wildfires is expected to increase 30% within the next 28 years, according to a February 2022 U.N. report.

Searing temperatures also swept across China's vast Yangtze River basin on Wednesday; firefighters tackled a forest fire near the tourist town of Datça in Turkey; and power demand in Texas hit an all-time high as consumers cranked up their air conditioners to escape the heat.

In Spain's western region of Extremadura bordering Portugal, firefighters battled a blaze that swept into Salamanca province in the region of Castile and Leon, burning more than 4,000 hectares.

Parts of the Extremadura, Andalusia and Galicia regions were on red alert for extreme heat, Spain's AEMET meteorology service said, adding the country's highest temperature on Wednesday stood at 45.6 degrees Celsius in Huelva province.