A terrible heatwave has gripped southern Europe, with temperatures in Spain reaching a high of 46 degrees Celsius (114.8 degrees Fahrenheit) and an alert has been issued for almost all of mainland France, The Guardian reports. 

Extreme heat, intensified by fossil fuel pollution, has scorched Portugal, Spain, France, Italy and Greece for days as southern Europe experiences its first heatwave of the summer.

The high temperatures have forced authorities in several countries to issue new health warnings and call in firefighters to prevent wildfires.

More than 50,000 people in Turkey have been evacuated from their homes because of the wildfires, according to the Interior Ministry's Disaster and Emergency Management Directorate.

The southern Spanish city is forecast to be more than 40 degrees hot for the next three days, with nighttime temperatures of at least 25 degrees through Thursday morning.

Doctors have expressed alarm at the combination of hot days and uncomfortably warm nights, which could put deadly stress on the human body.

In Italy, where 21 of 27 cities declared the hottest temperatures on Sunday, the number of hospitalizations in some of the hottest regions, such as Tuscany, increased by 20 percent. People have been advised not to go outside between 11am and 6pm. 

For the first time in the history of France, heat warnings have spread to almost the entire mainland of the country.

The French Meteorological Service has declared the second-highest “orange” danger level due to heat in 88% of administrative districts.