In Germany, where highs of 38C were expected on Saturday, the health minister urged vulnerable groups to stay hydrated.

"Heat and too little fluids can be deadly for older people," Karl Lauterbach tweeted.

"We need to keep an eye on the elderly and those with disabilities today."

Meanwhile, officials warned of wildfires across the western Mediterranean region as high temperatures and a long dry spell made for combustible conditions.

The European Commission's Copernicus Emergency Management Service said the fire risk was "extreme" and "very extreme" in much of Spain, the Rhone river valley in France, Sardinia, Sicily and parts of mainland Italy.

The 27-nation bloc has put 12 firefighting planes and a helicopter on standby to assist countries struggling with major blazes this summer.

Meteorologists in France described the situation as "really exceptional" and predicted that a peak of 43C on Saturday before thunderstorms brought cooler weather from the Atlantic.

Experts say the early heat wave is a sign of what's to come as climate change makes extreme temperatures usually seen only in July and August more likely in June too.

Australian Associated Press