Longer and more intense heat waves will pose a life-and-death threat in the coming decades across large swathes of South and Southeast Asia, along with areas straddling the equator in Africa and Latin America.

This heatwave comes as the country already grapples with power cuts that have hurt its economy in recent months, including its crucial apparel sector that accounts for more than 80% of its exports.

In an El Nino pattern, there is a higher chance of drier weather in Australia's east and it would likely be warmer than usual for the southern two-thirds of Australia.

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.

Similar weather patterns have caused flooding and landslides in the past, most notably in the summer of 2018, when more than 200 people were killed in western Japan.

The water services commission says most of the dams in the country have water levels of above 90%.

Southern Chinese provinces are expected to swelter under extreme heat and weather experts have already predicted another blistering summer, a repeat of last year's record-breaking more than two-month stretch.

The monsoon is the lifeblood of the country's US$3 trillion economy, Asia's third-largest, and delivers nearly 70% of the rain it needs to water farms and recharge reservoirs and aquifers.

The floods are the latest in a series of extreme weather events that have slammed Italy over the past year, as once exceptional disasters become a regular part of life.

Aid agencies and scientists have warned climate change is among the key factors accelerating humanitarian emergencies, while those impacted are some of the least responsible for CO2 emissions.

Muddy waters flowed through the streets washing over the roofs of parked cars, submerging some stores and forcing locals to flee to the top stories of their homes.

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.