Belgium’s record temperature was broken on Wednesday as temperatures soared in Western Europe.
The town of Kleine Brogel in Limburg province hit 38.9C (102F), beating the previous record set in 1947.
A Eurostar train broke down due to the extreme heat, trapping passengers.
Record temperatures were also close to be being broken in the Netherlands, while report from France said five deaths may have been linked to the heatwave.
The highest temperature recorded in Paris – 40.4C in 1947 – was expected to fall on Thursday.
Luxembourg is on red alert for the south and the capital – with top temperatures set to reach 40C on Wednesday and a potential 42C on Thursday.
How hot could it get?
Much of France has been issued with an orange alert – the second highest level of warning.
Météo France said Paris temperatures might hit new highs on Thursday. The record, set in 1947, stands at 40.4C.
Comparisons have been drawn with a heatwave France experienced in August 2003, during which heat contributed to almost 15,000 deaths.
The mercury is also expected to climb to 40C in a string of countries:
- In an unprecedented move, Belgium has issued a code red weather warning for the whole country
- Spain declared a red alert in its Zaragoza region, which was hit by devastating wildfires last month. The European Commission’s Copernicus Climate Change Service says the risk of wildfires is high in Spain and in Portugal
- In the Netherlands, the government activated its “national heat plan”
- In the UK, temperatures are predicted to exceed 35C, and could be the highest ever recorded
What preparations are being made?
To limit the heating of water used to keep its nuclear reactors cool, French energy firm EDF said it would be shutting two reactors at the Golftech nuclear power plant in the southern Tarn-et-Garonne region.
Ice foot baths and extra water points are being made available to cyclists competing in the Tour de France – which is entering its final week – to avoid dehydration.
The French government is outlawing animal transportation “for economic reasons” between 13:00 (11:00 GMT) and 18:00 in areas affected by heat alerts.
How high have temperatures been already?
The French weather service has reported temperatures of 42C in areas of the south-west. It is expected the heat will not dip below 20C for the rest of the week.
An intense heatwave swept through areas of Europe last month, making it the hottest June on record.
France set an all-time high-temperature record of 46C, according to the WMO, and new June highs were set in the Czech Republic, Slovakia, Austria, Andorra, Luxembourg, Poland, and Germany.
What about droughts?
The continent has also been hit by severe droughts, particularly in France, with no rainfall in many areas since last month’s heatwave.
A number of places in France have set new records for the lowest amount of rainfall ever recorded, Ms Nullis of the WMO said.
This has caused problems with nuclear energy facilities and agriculture – such as grape harvests for wine in the region and crops. Farmers in mountainous areas have been allowing cattle to graze on what are ski slopes in winter due to the effect of the drought on lower ground.
The government has imposed restrictions on water use in 73 regions and Paris has seen its driest period for almost 150 years.
France will send a request to the European Commission to bring forward a payment of €1bn ($1.12bn; £892m) to assist farmers hit by the recent weather.
Is climate change to blame?
Linking a single event to global warming is complicated. While extreme weather events like heatwaves occur naturally, experts say these will happen more often because of climate change.
Records going back to the late 19th Century show that the average temperature of the Earth’s surface has increased by about one degree since industrialisation.
A climatology institute in Potsdam, Germany, says Europe’s five hottest summers since 1500 have all been in the 21st Century.
Scientists are concerned that rapid warming linked to use of fossil fuels has serious implications for the stability of the planet’s climate.