A blistering heatwave sweeping through Europe on Wednesday brought blackouts to France and fears of heat stroke for Wimbledon tennis fans, but meant a range of interesting ice creams for the continent's zoo animals.

With temperatures pushing 40 degrees Celsius (104 degrees Fahrenheit), the UN warned heatwaves were growing more frequent and intense due to climate change, and called on more countries to put warning systems in place to inform people of the dangers.

At the Safaripark Beekse Bergen zoo in the Netherlands, staff had already put their emergency procedures in place -- including ice cubes for baboons, cold showers for the elephants, and special meat- and fruit-flavoured ice cream for the ring-tailed lemurs.

Not to be outdone, especially on the subject of ice cream, Italy's main zoo in Rome offered gelato to its orangutans with a choice of flavours including fresh fruit and vegetables, or dried figs topped with eggs and insects.

Humans were having a tougher time, with around a million homes in western France left without power overnight Tuesday after the heatwave moved in from Spain, and another blackout striking Brittany Wednesday morning, cutting electricity to 100,000 houses.

The Wimbledon tennis tournament in London saw the hottest day of play ever at 35.7 degrees Celsius, more than a degree hotter than the record set in 1976.

A ball boy collapsed and hot weather rules meant women players got a 10-minute break between the second and final sets, though there was criticism that men did not get the same break.

Defending champion Novak Djokovic remained unfazed: "It wasn't as bad as I thought," he said.

Elsewhere in the city, public fountains became impromptu beaches, with parents sunbathing on benches and children playing in the water in their swimming costumes behind King's Cross station.

Meanwhile in Brussels, it was hard to tell whether European Commission President Jean-Claude Juncker was sweating from the pressure of the Greek crisis or just the ambient temperature.

He joked with photographers at a press conference: "Every time I scratch myself, wipe my brow, you take a photo. Now I know what to do to end up in tomorrow's papers!"

- UN warning -

Another heatwave set to last at least nine days is expected to hit Spain on Friday and then spread to France, Italy, Germany and eastern Europe, the Spanish national weather office said.

Temperatures will be especially high on Monday, reaching 44 degrees Celsius in some Spanish regions, due to the arrival of hot winds blowing from Africa.

The extreme heat carries serious dangers, particularly to the elderly, sick and very young.

The last major hot spell in 2003 caused an estimated 70,000 deaths in Europe, and Portugal has already recorded around 100 deaths over the normal mortality rate since temperatures rose at the weekend, its health authority said.

The first death directly linked to the heat was reported in the British press after a father drowned while trying to save his young daughter cooling off in a river in the northern Cumbria region.

The elderly, sick, and those on certain medications are vulnerable because their bodies' heat regulation system can be impaired, leading to heatstroke.

And young children "produce more metabolic heat, have a decreased ability to sweat and have core temperatures that rise faster during dehydration," said Britain's National Health Service in a report.

The Muslim Council of Britain warned people fasting for Ramadan to take extra care, and said Islamic law allowed the sick and vulnerable to break the daytime fast during extreme conditions.

The UN called for heatwave warning systems that would highlight the health hazards and inform people what they should do to protect themselves.

France and Belgium are among the countries that introduced such a system after the deadly 2003 heatwave.

But elsewhere, such systems are not common, Diarmid Campbell-Lendrum of WHO told AFP, voicing concern about places like Pakistan, where more than 1,200 people have died amid soaring temperatures in the south of the country.

That crisis came a month after neighbouring India suffered its own deadly heatwave which killed more than 2,000 people.

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