Outdoor public events have been banned in an area of France as a record-breaking heatwave swept across Europe on Saturday.
Concerts and large public gatherings have been called off in the Gironde region around Bordeaux.
Parts of France hit 40C on Saturday.
Scientists say periods of intense heat are becoming more frequent and longer lasting as a result of global warming.
Spain, Italy and the UK are also experiencing high temperatures.
In Gironde, officials said public events, including some of the official 18 June Resistance celebrations, will be prohibited "until the end of the heat wave".
Indoor events at venues without air-conditioning are also banned.
"Everyone now faces a health risk", local official Fabienne Buccio told Bleu radio.
The French interior ministry warned people to be extremely careful and not expose themselves to the weather.
State forecaster Meteo France said it was the earliest hot spell ever to hit the country, which has been caused by a mass of hot air moving from north Africa.
Temperatures could hit 39C in Paris and droughts have also raised the risk of wildfires, the forecaster said.
The increased use of air-conditioners and fans was forcing France to import electricity from neighbouring countries, grid operator RTE said.
In Spain, which has just experienced its hottest May since the beginning of the century, temperatures are forecast to hit highs of 43C this weekend, the Aemet weather service said.
Forest fires have burned 22,240 acres of land in the northwest Sierra de la Culebra region, forcing some 200 people from their homes, regional authorities said.
More than 3,000 people were evacuated from the Puy du Fou theme park in central Spain due to a fierce fire nearby.
Water is so low in large stretches of Italy's largest river, the Po, that people are able to walk through the middle of the expanse of sand and wartime shipwrecks are resurfacing.
In the UK, temperatures are expected to reach 33C in southern England, while a level three heat-health alert has been issued for London.
Temperatures are due to relent slightly from Sunday with thunderstorms forecast in parts of France and elsewhere in Europe.
Experts warned that the high temperatures were caused by worrying climate change trends.
"As a result of climate change, heatwaves are starting earlier," said Clare Nullis, a spokeswoman for the World Meteorological Organisation in Geneva.
"What we're witnessing today is unfortunately a foretaste of the future" if concentrations of greenhouse gases in the atmosphere continue to rise and push global warming towards 2 Celsius from pre-industrial levels."