Red alerts have been issued for 16 cities across Italy as extreme heat continues to affect southern Europe.
The alerts, which indicate risks even for healthy people, apply to tourist hotspots including Rome, Florence, and Bologna for the coming days.
The heatwave has already lasted longer than usual and night-time temperatures have remained high.
More high temperatures are expected in Europe next week as another heatwave approaches.
Periods of intense heat occur within natural weather patterns, but globally they are becoming more frequent, more intense and are lasting longer due to global warming.
The Italian government has advised anyone in the areas covered by Saturday’s red alerts to avoid direct sunlight between 11:00 and 18:00, and to take particular care of the elderly or vulnerable.
In Rome, tour guide Felicity Hinton, 59, told the BBC the soaring temperatures combined with overcrowding has made it “nightmarish” to navigate the city.
“It’s always hot in Rome but this has just been consistently hot for a lot longer than normal,” she said.
Meanwhile, Greece has hit temperatures of 40C (104F) or more in recent days. The Acropolis in Athens – the country’s most popular tourist attraction – was closed during the hottest hours of Friday and Saturday to protect visitors.
Matt Finden, 51, from Vancouver, Canada, and his family were among the last tourists to visit The Acropolis before it closed.
“It was incredible up there. But along the way we saw people passed out getting medical attention, sitting on the backs of ambulances and even vomiting from heatstroke,” he told the BBC.
The Red Cross has been offering water and first aid at the site, which sits on a rocky hilltop and offers little shade to visitors.
There are also fears of a greater risk of wildfires, especially in areas with high winds. Greece suffered major wildfires in 2021 in another exceptional heatwave.
Elsewhere, a forest fire on the Spanish island of La Palma forced the evacuation of at least 500 people, Reuters news agency reported.
The fire broke out in the early hours of Saturday morning in El Pinar de Puntagorda, destroying at least 11 houses, Fernando Clavijo, president of the Canary Islands, said.
High temperatures have also been reaching into central parts of Europe, with Germany and Poland among countries affected.
Czech Republic’s meteorological office issued a warning that temperatures over the weekend could go above 38C, which is exceptionally high for the country.
Highs of up to 47C are expected across some parts of southern Spain, south-eastern Italy and possibly Greece later in the week. It is likely that some city records will be broken.
In the UK, however, heavy showers and gusty winds are expected in parts of England on Saturday.
Meteorologists said this was because the southern shift of the jet stream, which was fuelling the hot weather in Europe, was also drawing low-pressure systems into the UK – bringing unsettled and cooler weather.
The current heatwave in Europe has been named Cerberus by the Italian Meteorological Society, after the three-headed monster that features in Dante’s Inferno.
Italian weather forecasters are warning that the next heatwave – dubbed Charon after the ferryman who delivered souls into the underworld in Greek mythology – could push temperatures back up above 40C next week.
Heatwaves are also being seen in parts of the US, China, North Africa and Japan.
Last month was the hottest June on record, according to the EU’s climate monitoring service Copernicus.
The hottest temperature ever recorded in Europe was 48.8C in Sicily in August 2021.
Extreme weather resulting from warming climate is “unfortunately becoming the new normal”, the World Meteorological Organisation (WMO) has warned.