Record temperatures across Europe have claimed the lives of at least 1,500 people, with train tracks buckling and fires raging across the continent.
Portugal authorities have reported more than 1,000 heat-related deaths while estimates from the Carlos III Health Institute place Portugal's death toll at 510.
The temperature in the UK exceeded 40 degrees Celsius for the first time in history on Tuesday, with a major incident declared in London.
The Met Office said the provisional record, which still needed to be confirmed, was recorded near midday at London's Heathrow Airport, where the temperature surpasses the previous high of 38.7C recorded in 2019.
Average July temperatures in the UK range from a daily high of 21C to a night-time low of 12C, and few homes or small businesses have air conditioning.
At least five people were reported to have drowned across the UK — in rivers, lakes and reservoirs — while trying to cool off.
A huge chunk of England, from London in the south to Manchester and Leeds in the north, was under the country's first warning of "extreme" heat on Tuesday, meaning there was a danger of death for even healthy people, as the hot, dry weather that had scorched mainland Europe for the past week moved north.
London-based fire safety expert Stephen Mackenzie told ABC NewsRadio the London Fire Service had been deployed to "10 or more" simultaneous bushfires, with hundreds of firefighters on the ground.
He said the UK was now facing major bushfires and structural fires in whole neighbourhoods, which was "almost unheard of in the UK".
"We don't normally see this level of intensity in the UK," Mr Mackenzie said.
"We certainly don't see whole neighbourhoods being wiped off the street.
"And we can only imagine the heat intensity and the heat stress that these firefighters have experienced today, and we're not out of the danger zone."
Mr Mackenzie said people in London were hoping a cold front coming from the Atlantic could bring rain and dissipate the heat.
He said local communities were still in shock over the fire damage, and he hoped the extent of the disaster would push the government to re-evaluate its current wildlife strategy and better prepare for next time.
More than 30 wildfires continued to ravage parts of Spain, meanwhile, with authorities paying special attention to four blazes in Castile, Leon and Galicia.
Risk remains as heat lingers
The World Meteorological Organization (WMO) believes Europe's heatwave may have already peaked, but temperatures could remain above average for another week.
"The question that everybody is asking looking ahead is, 'When is this going to end?'" Robert Stefanski, chief of applied climate services at the WMO, said.
"Unfortunately, looking at all the models from all our partners at a national and regional level, possibly not until the middle of next week."
The head of Portugal's health authority, Graca Freitas, warned the country needed to gear up to cope with the effects of climate change as temperatures continued to rise.
"Portugal … is among one of the areas of the globe that could be [more] affected by extreme heat," she said.
"We have to be more and more prepared for periods of high temperatures."
A researcher at Lisbon University's faculty of sciences said the data showed those most likely to die due to heatwaves were elderly people.
He said the number of deaths in the future would depend, among other things, on the preventive measures people adopted to protect themselves, how care homes tended to their residents, and how infrastructure was adapted.
High temperatures, as well as the ongoing drought and poor forest management, have been blamed for several wildfires sweeping across Portugal.
'We have nothing'
As wildfires raged across Portugal, Spain and France, authorities warned there was a risk of more blazes as tinder-dry conditions persisted.
Spain was on Tuesday facing the last day of a more than week-long heatwave, which has caused more than 510 heat-related deaths, according to estimates from the Carlos III Health Institute.
In Tabara, locals said the driver of an excavator was trying to dig a trench between a fire and buildings when flames surrounded the vehicle.
TV footage showed him emerging from the blaze, tripping, then scrambling to his feet as people shouted out to him and a firefighter ran up to help.
The driver was airlifted to hospital with burns, witnesses said, though there were no detailed reports on his condition.
In El Pont de Vilomara in Catalonia, evacuees gathered outside a civic centre. Among them was retiree Onofre Munoz, 69, who said his home and van were destroyed by a blaze.
"We bought the van when I retired and now it's totally scorched," he said.
"We have nothing."
ABC/wires
