Millions suffered through intense heat Wednesday as fires raged, health worries mounted and the world appeared headed for its hottest month of July on record.

As temperature records tumbled on three continents, experts pointed the finger at climate change driven by the burning of fossil fuels, saying global warming had a key role in destructive weather.

Governments and the World Health Organization issued warnings as vulnerable parts of the population suffered.

In Greece, two forest fires, fanned by strong winds, were raging to the west of Athens, and another on the tourist island of Rhodes where residents had to decide whether to flee.

"I am not leaving. I started building this house when I was 27 years old by myself," said Dimitris Michaelous, a resident in the fire-threatened town of Pournari.

Greece's firefighters said Romania, Slovakia and Poland would send some 230 firefighters to help it tackle the blazes.

Polish fire services said 149 firefighters were on their way to Greece -- 2,000 kilometres (1,250 miles) away -- aboard 49 vehicles.

France recorded temperatures of up to 40 degrees Celsius (104 degrees Fahrenheit) in the country's south, including on the Mediterranean holiday island Corsica.

Beijing broke a 23-year-old record with 27 consecutive days of temperatures above 35 degrees Celsius.

- 'My skin is burning' -

"At noon, it feels like the sun is roasting my legs, it feels like my skin is burning," said Qiu Yichong, a 22-year-old student.

Han Weili, a delivery driver, told AFP: "Sometimes when it is very hot, I feel a little confused or dizzy."

The Beijing government urged the elderly to stay indoors and children to shorten outdoor playtime to reduce exposure to the heat and ground-level ozone pollution.

People were cranking up air conditioning, leading to a surge in energy demand.

The World Health Organization said the extreme heat was straining healthcare systems, hitting older people, infants and children.

The WHO said it was particularly concerned about people with cardiovascular diseases, diabetes and asthma.

In the Canary Islands, some 400 firefighters battled a blaze that has ravaged 3,500 hectares of forest and forced 4,000 residents to evacuate, with authorities warning people to wear face masks outside due to poor air quality.

Temperatures were also ferocious in other parts of Spain, with three regions on red alert.

Coastal waters around Spain have hit a record high temperature for this time of the year, the national weather office said Wednesday.

The Italian islands of Sardinia and Sicily have been forecast to possibly surpass a continent-wide record of 48.8C recorded in Sicily in August 2021.

At Lanusei, near Sardinia's eastern coast, a children's summer camp was restricting beach visits to the early morning and banning sports, teacher Morgana Cucca told AFP.

- 'Better at the beach' -

Many throughout Italy sought escape by the sea, including outside Rome, where the heat hit 40C.

"You can at least get a little wind from the sea," said Virginia Cesario, 30, at the Focene beach near the capital.

"This has become the new normal," said Fabrizio Carozza, a 26-year-old office employee from Belgium.

In North America, meanwhile, tens of millions of people woke up to another scorcher Wednesday, having experienced dangerous heat the previous day.

- 'Running out of ways' -

In the town of San Angelo, Texas, where temperatures were expected to reach 108F (42C), the National Weather Service said it was "running out of ways to say that it's gonna be hot out there today."

"We implore you to continue to practice heat safety," the agency said on Twitter.

And in Arizona, the mercury at Phoenix Sky Harbor Airport again reached 110F on Tuesday, breaking the previous record of 18 consecutive days at or above that temperature, set in 1974.

Even Iraq, used to average July temperatures of around 32C, found it hard to cope with the heat surge, prompting the mayor of Basrah in the south to give civil servants a day off Thursday when 50C or more is forecast.

The world is on track for its hottest July since measurements began, the European Union's climate observatory told AFP Wednesday.

"The first 15 days of July have been the warmest 15 days on record," said Carlo Buontempo, director of the Copernicus Climate Change Service(C3S).

The heat waves across Europe and the globe are "not one single phenomenon but several acting at the same time", said Robert Vautard, director of France's Pierre-Simon Laplace climate institute.

"But they are all strengthened by one factor: climate change."

AFP