Authorities temporarily closed the Dardanelles Strait to shipping, creating a queue of about 100 cargo ships, to allow helicopters and planes to scoop up water to contain a forest fire in the area raging for a second day.

Firefighters say they are investigating whether the bodies, found near a shack south of the village of Avantas, were migrants.

Officials in New York City, Washington DC, Philadelphia and other big cities urged people to avoid working or playing outside, to drink plenty of fluids and to check on loved ones and neighbors.

The growing frequency and intensity of severe weather is symptomatic of global, human-driven climate change that is fueling extremes, experts say, with current heatwaves expected to persist through August.

Greece has been particularly hard hit by fires, with authorities evacuating more than 20,000 people in recent days from homes and resorts in the south of the holiday island of Rhodes.

Extreme weather has caused havoc across the planet, with temperatures breaking records in China, the US and southern Europe, sparking forest fires, water shortages and a rise in heat-related hospital admissions.

Wild weather swings have gripped China since April, causing deaths, damaging infrastructure and wilting crops as well as raising fears of its ability to cope with climate change.

Overnight minimum temperatures were also set to reach new highs, according to the WMO, creating risks of increased cases of heart attacks and deaths.

Heatwaves in June have become more frequent in recent years, part of a global pattern of rising temperatures, widely attributed by scientists to human activity.

Climate change is making heatwaves hotter and more frequent - a trend that, when combined with urban heat islands, poses risks including increased deaths from heat stress to vulnerable populations like the elderly.

Most of southern China is expected to be hit by temperatures of more than 35 Celsius, with temperatures in some areas exceeding 40C, reports say.

Continued use of oil, coal and gas to power homes, cars and the world's economy results in the release of gases that blanket the planet, trapping ever more of the sun's energy in the atmosphere.