Global temperatures were soaring to historic highs as the world's two biggest carbon emitters, the United States and China, sought on Monday to reignite talks on climate change.
With scientists saying the target of keeping global warming within 1.5 degrees of pre-industrial levels is moving beyond reach, evidence of the crisis was everywhere.
A remote town in China's arid northwest, Sanbao, registered a national record of 52.2 degrees.
Wildfires in Europe raged ahead of a second heat wave in two weeks that was set to send temperatures as high as 48 degrees.
And nearly a quarter of the U.S. population fell under extreme heat advisories, partly due to a heat dome that has settled over western states.
"In many parts of the world, today is predicted to be the hottest day on record," tweeted Tedros Adhanom Ghebreyesus, director-general of the World Health Organisation.
"The #ClimateCrisis is not a warning. It’s happening. I urge world leaders to ACT now."
Ahead of meeting Chinese counterpart Xie Zhenhua in Beijing, U.S. climate envoy John Kerry urged China to partner with the United States to cut methane emissions and coal-fired power.
Prolonged high temperatures in China are threatening power grids and crops and raising concerns about a repeat of last year's drought, the most severe in 60 years.
Typhoon Talim was gaining strength and due to make land at night along China's southern coast, forcing the cancellation of flights and trains in the regions of Guangdong and Hainan.
In South Korea, torrential rains left 40 people dead as river levees collapsed causing flash floods. They followed the heaviest recorded rain in the capital Seoul last year.
An anticyclone nicknamed Charon - who in Greek mythology was the ferryman of the dead - could cause Europe to break its highest recorded temperature of 48.8 degrees, possibly on the Italian island of Sardinia, according to Italy's Air Force weather service.
The high temperatures are especially risky for people like teenage sisters Matilde and Angelica Aureli from Rome, who during extreme heat can only venture outside after 9 p.m. because of their albinism. The genetic condition affects the protective pigment melanin in hair, skin and eyes.
"In the summer, it is getting hotter year by year... it's actually very scary as an experience because for people with albinism, the sun keeps getting worse," Matilde said.
In Spain, temperatures could rise to as high as 44 degrees in some regions and will not fall below 25 degrees at night, increasing the probability of wildfires, said Ruben del Campo, a spokesperson for state weather agency AEMET.
However, a forest fire on the island of La Palma in the Canaries that forced the evacuation of 4,000 people was being brought under control as temperatures fell, local official Sergio Rodriguez said in an interview on TVE.
The heat dome across the western United States also helped to generate heavy rains in the northeast, claiming at least five lives. The heat warnings spread as far as Florida.
In California's Death Valley, tourists gathered in Furnace Creek on Sunday in anticipation of witnessing the hottest recognised temperature on earth: 56.7 degrees in 1913, according to the World Meteorological Organization.
