Temperatures are expected to reach record highs in Italy and the World Meteorological Organization has warned of an increased risk of deaths as heatwaves and extreme weather grip parts of Europe, Asia and the United States.

The Mediterranean island of Sardinia could see highs of more than 47 degrees Celsius and forecasters said temperatures could hit 40C in several Italian cities, including 42C to 43C in the Lazio region that includes Rome.

With baking temperatures hitting Europe during the peak summer tourist season, the World Meteorological Organization (WMO) said the heatwave in the northern hemisphere was set to intensify in coming days and warned of an increased risk to health.

An estimated 61,000 people might have died in heatwaves last year in Europe alone.

Heatwaves this summer, which saw temperatures climb to 53C in California's Death Valley and more than 52C in China's northwest, have coincided with wildfires from Greece to the Swiss Alps and deadly flooding in India and South Korea.

They have added fresh urgency to talks this week between the US and China, the world's top greenhouse gas polluters.

US climate envoy John Kerry met Chinese officials in Beijing and expressed hope climate co-operation could redefine troubled ties between the two powers.

Chinese President Xi Jinping stressed Beijing's commitment to carbon neutrality and a carbon peak was certain but it would not be influenced by others.

"Temperatures in North America, Asia, and across North Africa and the Mediterranean will be above 40C for a prolonged number of days this week as the heatwave intensifies," the WMO said.

Overnight minimum temperatures were also expected to reach new highs, the WMO said, creating the risk of increased cases of heart attacks and deaths.

"Whilst most of the attention focuses on daytime maximum temperatures, it is the overnight temperatures which have the biggest health risks, especially for vulnerable populations," it said.

The heat in Europe could also prompt a lasting shift in tourist habits, with more people choosing cooler destinations or travelling in spring or autumn, tourism organisations predicted.

Scientists have long warned that climate change, caused by greenhouse gas emissions mainly from burning fossil fuels, will make heatwaves more frequent, severe and deadly.

They say governments need to take drastic action to reduce emissions to prevent climate catastrophe.

The European Union's Copernicus Climate Change Service says 2022 and 2021 were the continent's hottest summers on record.

Europe's highest recorded temperature of 48.8C was registered in Sicily two years ago.

In Italy, tourists have tried to keep cool by splashing water on themselves from Rome's fountains and standing under giant fans set up outside the Colosseum.

Some were forced to queue for taxis for more than an hour in the scorching heat outside the central railway station in Rome due to the capital's chronic shortage of cabs.

The health ministry has issued red weather alerts - signalling a possible health threat for anyone exposed to the heat - for 20 of the country's 27 main cities on Tuesday, with the number expected to rise to 23 on Wednesday.

"It is not ruled out that we will exceed 47 degrees, and there could be some places in Sulcis and Campidano (areas in southern Sardinia) that could make us record an even higher value," said Carlo Spanu, from the Italian air force's weather service.

"Our historical record is 47.7 degrees.

"Nothing prevents us from exceeding or equalling it."

In Spain, areas of the northeastern regions of Catalonia and Aragon and the Mediterranean island of Mallorca were on alert for temperatures of between 42C and 44C on Tuesday.

In China, trees fell on vehicles, a whale washed ashore and a freezer full of ice cream floated off in floods as Typhoon Talim made its way across southern provinces on Tuesday, the first to make landfall in the country this year.