The mercury was pushing 40C across much of northern Europe on Wednesday as a blistering heatwave saw blackouts in France and emergency ice cream handed out to lemurs at a Dutch zoo.

As the hot front continued its sweep up from Africa, 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.  

Around a million homes in western France were left without power overnight Tuesday after the heatwave moved in from Spain, and another blackout struck the western Vannes region Wednesday morning, cutting electricity to 100,000 houses.

"At this temperature, we can't stay on a roof. It's overwhelming," said Laurent Floux, a roofer in Paris, who got his team working at the crack of dawn to avoid the worst of the heat.

Many schools across Europe shifted their start times to keep children out of the sun's glare.

Rotterdam's football club Feyenoord also said it was shifting training to later in the day.

Meanwhile in central London, 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.

The first death linked to the heatwave 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 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.

- UN warning -

The last major hot spell in 2003 caused an estimated 70,000 deaths in Europe -- particularly among the elderly, sick and very young.

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

"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 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.