Record heat is forecast around the world from the United States, where tens of millions are battling dangerously high temperatures, to Europe and Japan, in the latest example of the threat from global warming.

According to Yahoo News, Italy faces weekend predictions of historic highs with the health ministry issuing a red alert for 16 cities including Rome, Bologna and Florence.

The meteo centre warned Italians to prepare for “the most intense heatwave of the summer and also one of the most intense of all time”.

The thermometer could hit 40 degrees Celsius (104 Fahrenheit) in Rome by Monday and even 43C on Tuesday, smashing the record 40.5C set in August 2007.

The islands of Sicily and Sardinia could wilt under temperatures as high as 48C, the European Space Agency warned — “potentially the hottest temperatures ever recorded in Europe”.

“Parts of the country could see highs as much as 44C on Saturday,” according to the national weather service EMY. The central city of Thebes sweated under 44.2C on Friday.

The Acropolis, Athens’s top tourist attraction, closed for a second day straight Saturday during the hottest hours with 41C expected, as were several parks in the capital.

Access to the UNESCO-listed archaeological site dating to antiquity is being suspended from midday to early evening “to protect workers and visitors”, the culture ministry said.

Regions of France, Germany, Spain and Poland are also baking in searing temperatures. China has for weeks been hit by extreme weather — from heavy rains to suffocating heatwaves.

Parts of eastern Japan are also expected to reach 38 to 39C (100.4 to 102.2F) on Sunday and Monday, with the meteorological agency warning temperatures could hit previous records.

But relentless monsoon rains have reportedly killed at least 90 people in northern India, after burning heat.

The Yamuna river running through the capital New Delhi has reached a record high of 208.66 metres, more than a metre over the flood top set in 1978, threatening low-lying neighbourhoods in the megacity of more than 20 million people.