Heatwaves are becoming more intense and frequent worldwide because of human-caused climate change, scientists say, and Japan is no exception.

This "is the first time since the survey started" in 1875 that such a run has been recorded, the Japan Meteorological Agency told AFP, saying that Wednesday marked the 10th day of the heat streak.

It came after a town on the northern island of Hokkaido was deluged by a record level of rainfall on Tuesday, according to public broadcaster NHK.

Toyotomi logged more than a month's worth of rainfall in an average August in just 12 hours, it said.

And in western Yamaguchi prefecture nearly 400 households in Hagi City were urged to evacuate, NHK added, due to a high risk of landslides.

Japan this year had its hottest June and July since data collection began in 1898 and in August the country logged its highest temperature ever, with the mercury hitting 41.8C in the central city of Isesaki.

Japanese officials urge the public to seek shelter in air-conditioned rooms during the summer to avoid heatstroke.

The elderly in Japan -- which has the world's second-oldest population after Monaco -- are particularly at risk.

Last week more than 8,400 people were hospitalised in Japan, according to the Fire and Disaster Management Agency, and 12 of them died.

- Impact on health and productivity -

Japan's summer last year was the joint hottest on record, equalling 2023, and was followed by the warmest autumn since records began 126 years ago.

Experts warn Japan's beloved cherry trees are blooming earlier due to the warmer climate -- or sometimes not fully blossoming -- because autumns and winters are not cold enough to trigger flowering.

The famous snowcap of Mount Fuji was absent for the longest recorded period last year, not appearing until early November, compared with the average of early October.

The speed of temperature increases across the world is not uniform.

Of the continents, Europe has seen the fastest warming per decade since 1990, followed closely by Asia, according to global data from the US National Oceanic and Atmospheric Administration (NOAA).

The United Nations warned last week that rising global temperatures are having an ever-worsening impact on the health and productivity of workers, with manual workers in sectors such as agriculture, construction and fisheries particularly hard hit.

The UN's health and climate agencies said in a report that worker productivity dropped by two to three percent for every degree above 20C.

The related health risks include heatstroke, dehydration, kidney dysfunction, and neurological disorders.