Spain's prime minister said "more than 500 people died" during a 10-day heatwave as Europe counts the cost of a record period of extreme temperatures.

Climate change protesters said the scorching weather should be a wake-up call for the continent.

"This has nothing to do with ideologies, but with a reality, with a climatic emergency that the planet is living through," said Spanish Prime Minister Pedro Sanchez.

Speaking against a backdrop of charred trees and burnt ground in the hard-hit northeastern Zaragoza region, he urged people to exercise "extreme caution".

Sanchez cited figures released by the Carlos III Health Institute, which estimates the number of heat-related fatalities based on the number of excess deaths compared to the average in previous years.

The institute has stressed these figures are a statistical estimate and not a record of official deaths.

Meanwhile, Greek firefighters gained the upper hand in a battle against a wildfire raging for a second day in mountainside suburbs north of Athens that had forced hundreds of people to flee, an official said.

"For the most part, the fire is in decline," fire department spokesman Yiannis Artopios told reporters.

Greece had been spared the blistering heat wave experienced in western Europe, but flames fanned by high winds were threatening the suburbs of
Penteli, Pallini, Anthousa, and Gerakas, are home to tens of thousands of people.

"The fire was scorching our backs, we left in the nick of time. Had we stayed another 30 seconds it would have burned us," a Pallini resident who lost his car and shed to the flames told ERT television.

"The civil protection authority was late in alerting us," he said.

In France, firefighters brought twin blazes near the southwestern city of Bordeaux under control.

Temperatures of more than 40 degrees Celsius (104 degrees Fahrenheit) over previous days have spelled misery for millions and shattered heat records.

Cooler air swept in Wednesday, bringing relief to people from Portugal to Britain, but thousands of firefighters continued to tackle blazes that have broken out in multiple countries after months of drought-like conditions.

"Our assessment is generally positive. The situation improved overnight," French fire service spokesman Arnaud Mendousse told AFP from the southwestern Gironde region where two huge blazes have engulfed 20,600 hectares (50,900 acres) of tinder-dry forest since last week.