Millions of people across three continents suffered under a sustained spell of dangerous heat Wednesday as fires raged, health worries mounted and temperature records tumbled.

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 issued safety warnings, including in Greece which was among nations battling wildfires.

Two forest fires, fanned by strong winds, were raging to the west of Athens, while another broke out on the tourist island of Rhodes -- where locals 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.

The Greek government pleaded with the population to be extremely careful to not spark new fires.

France said on Wednesday temperatures of up 40 degrees Celsius (104 degrees Fahrenheit) were expected in parts of the country's south, including on the Mediterranean holiday island Corsica.

A high of 29.5C was recorded in the French Alpine ski resort of Alpe d'Huez, while 40.6C had been recorded for the first time in Verdun in the foothills of the Pyrenees.

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 has 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 in offices, homes and restaurants to stay cool, leading to a surge in energy demand.

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, as well as in Italy.

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 forbidding sports, teacher Morgana Cucca told AFP.

- 'Better at the beach' -

In the Sardinian capital of Cagliari, pharmacist Teresa Angioni said patients were complaining of heat-related symptoms.

"They mainly buy magnesium and potassium supplements and ask us to measure their blood pressure, which is often low," Angioni said.

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

"Certainly it's better at the beach, 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 back office employee from Belgium. "It's getting hotter and hotter."

In north America, meanwhile, tens of millions of Americans 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 and try to stay cool," 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.

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."

The record-setting heat came as US climate envoy John Kerry met with Chinese officials in Beijing, with the world's two largest polluters reviving stalled diplomacy on reducing planet-warming emissions.

Speaking Tuesday at Beijing's Great Hall of the People with China's top diplomat Wang Yi, Kerry called for "global leadership" on climate issues.