Heatwaves like the one stifling western Europe are becoming more frequent and the trend is set to continue until at least the 2060s, the United Nations said Tuesday.

The current heatwave should act as a wake-up call for countries pumping ever more carbon dioxide into the atmosphere, the UN's World Meteorological Organization said.

"They are becoming more frequent and this negative trend will continue... at least until the 2060s, independent of our success in climate mitigation efforts," WMO chief Petteri Taalas told a press conference in Geneva.

"Thanks to climate change we have started breaking records... In the future these kinds of heatwaves are going to be normal, and we will see even stronger extremes," he added.

"Emissions are still growing and therefore it's not sure that we would see the peak in the 2060s if we are not able to bend this emission growth development, especially in the big Asian countries which are the largest emitters."

The WMO held a joint press conference with the World Health Organization, its sister UN agency, about the fierce heatwave hitting western Europe.

The heatwave fuelled ferocious wildfires before sweeping north and pushing temperatures in Britain over 40 degrees Celsius (104 degrees Fahrenheit) for the first time.

"We are expecting the peak to be today across France, the UK, possibly even Switzerland," said Robert Stefanski, the WMO's applied climate services chief.

"And the question everybody's asking, looking ahead, when will this end? Unfortunately, looking at all the models... possibly not until the middle of next week."

Europe's heat record was broken last year when the thermometer hit 48.8C in Sicily in southern Italy.

"Our concern is that this is happening with shorter time periods between these records," Stefanski said.

Greece's record temperature had stood since 1977 before it was broken in 2021 and similar temperatures were being reached this year, he said.

Maria Neira, the WHO's environment, climate change and health director, recalled how the 2003 European heatwave cost more than 70,000 lives.

"This heat will compromise the capacity and the ability of our bodies to regulate our internal temperature. And this can result in a cascade of illnesses, starting obviously with heat cramps, heat exhaustion, heatstroke, hyperthermia."