Much of Western Europe is expected to face record-breaking temperatures again, with its second heatwave in a month set to reach its peak.
A red alert has been issued in Northern France - with temperatures of 41C forecast in Paris.
The UK is expecting 39C heat and trains have been ordered to run more slowly to stop rail tracks buckling in the heat.
Belgian, German and Dutch temperature records could be broken for the second time in two days.
"Climate change has increased the likelihood and severity of heatwave episodes across Europe," the UK's national weather service said.
What sort of temperatures are we expecting?
Authorities have launched a red alert - the highest state of alert - in the Paris region and 19 other districts, and say temperatures could reach 42-43C in parts of the country.
Belgium, Germany and the Netherlands had already recorded their highest-ever temperatures on Wednesday - of 39.9C, 40.5C and 39.3C respectively.
But forecasters believe the mercury could soar even higher on Thursday, and the Netherlands could see a new record of 40C in the south-east.
What's the impact going to be?
In France, officials have warned people to avoid travelling, and to work from home if possible. Children's nurseries have also been closed.
The chief architect responsible for restoring the Notre-Dame has warned that the extreme heat could lead to the cathedral roof collapsing if the joints and masonry holding up the roof dry up.
French reports suggest five deaths might have been linked to the heatwave so far,