ROME/BEIJING: Italy put 23 cities on red alert as it reckoned with another day of scorching temperatures on Wednesday, with no sign of relief from the wave of extreme heat, wildfires and flooding that has wreaked havoc from the United States to China.

The heat wave has hit southern Europe during the peak summer tourist season, breaking records - including in Rome - and bringing warnings about an increased risk of deaths.

Wildfires burned for a third day west of the Greek capital, Athens, and firefighters raced to keep flames away from coastal refineries.

Fanned by erratic winds, the fires have gutted dozens of homes, forced hundreds of people to flee and blanketed the area in thick smoke. Temperatures could climb to 43 Celsius (109 Fahrenheit) on Thursday, forecasters said.

Extreme weather was also disrupting life for millions of Americans. A dangerous heat wave was holding an area stretching from Southern California to the Deep South in its grip, bringing the city of Phoenix its 20th straight day with temperatures of 110 degrees Fahrenheit or higher.

Meanwhile, Tropical Storm Calvin lashed Hawaii, raising the potential for flash flooding and dangerous surf on the Big Island.

In Texas, at least nine inmates in prisons without air conditioning have suffered fatal heart attacks during the extreme heat this summer, the Texas Tribune newspaper reported. Another 14 have died during periods of extreme heat due to unknown causes.

A Texas Department of Criminal Justice spokesperson said preliminary findings of the deaths indicate that heat was not a factor in the fatalities. Nearly 70 of the 100 prisons in Texas are not fully air conditioned.

TEMPERATURES SOAR IN CHINA, ITALY

In China, which was hosting U.S. climate envoy John Kerry for talks, tourists defied the heat to visit a giant thermometer showing surface temperatures of 80 Celsius (176 Fahrenheit).

In Beijing, which set a new record as temperatures remained above 35 Celsius (95 Fahrenheit) for the 28th day in a row, Kerry expressed hope that cooperation to combat global warming could redefine troubled ties between the two superpowers, both among the top polluters.

Temperatures remained high across much of Italy on Wednesday, where the health ministry said it would activate an information hotline and teams of mobile health workers visited the elderly in Rome.

"These people are afraid they won't make it, they are afraid they can't go out," said Claudio Consoli, a doctor and director of a health unit.

Carmaker Stellantis STLAM.MI said it was monitoring the situation at its Pomigliano plant near Naples on Wednesday, after temporarily halting work on one production line the day before when temperatures peaked.

Workers at battery-maker Magneti Marelli threatened an 8-hour strike at their central Italian plant in Sulmona. A joint statement by the unions said "asphyxiating heat is putting at risk the lives of workers".

While the heat wave appears to be subsiding in Spain, residents in Greece were left surveying the wreckage of their homes after the wildfires.

"Everything burned, everything. I will throw it all," said Abbram Paroutsidis, 65.

Scientists have long warned that climate change, caused by greenhouse gas emissions mainly from burning fossil fuels, will make heat waves more frequent, severe and deadly and have called on governments to drastically reduce emissions.

In Germany, the heat wave sparked a discussion on whether workplaces should introduce siestas for workers.

"While the current heat wave is expected to last until around 26 July, another period of extreme temperatures may follow if the heat dome persists," said Florian Pappenberger, Director of Forecasts at ECMWF.

HEAT AND FLOODS IN ASIA

In South Korea, heavy rain has pummelled central and southern regions since last week. Fourteen deaths occurred in an underpass in the city of Cheongju, where more than a dozen vehicles were submerged on Saturday when a river levee collapsed. In the southeastern province of North Gyeongsang, 22 people died, many from landslides and swirling torrents.

In northern India, flash floods, landslides and accidents related to heavy rainfall have killed more than 100 people since the onset of the monsoon season on June 1, where rainfall is 41% above average.

The Yamuna River reached the compound walls of the Taj Mahal in Agra for the first time in 45 years, submerging several other historical monuments, and flooded parts of the Indian capital.

The Brahmaputra River, which runs through India's Assam state, burst its banks this month, engulfing almost half of the Kaziranga National Park - home to the rare one-horned rhino - in waist deep water.

A wall collapse from monsoon rains killed at least 11 construction workers in neighboring Pakistan.

Iraq's southern Basra governorate, with a population of around 4 million, said government work would be suspended on Thursday as temperatures hit 50 Celsius (122 Fahrenheit). In Iraq's northern city of Mosul, farmers said crops were failing due to heat and drought.

The unprecedented temperatures have added new urgency for nations around the globe to tackle climate change. With the world's two biggest economies at odds over issues ranging from trade to Taiwan, Kerry told Chinese Vice-President Han Zheng on Wednesday that climate change must be handled separately from broader diplomatic issues.

"It is a universal threat to everybody on the planet and requires the largest nations in the world, the largest economies in the world, the largest emitters in the world, to come together in order to do work not just for ourselves, but for all mankind," Kerry told Han.