Seventeen heat records were broken in Japan on Monday, the weather agency said, after the country sweltered through its hottest ever June and July.

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

The city of Komatsu, in the central region of Ishikawa, saw a new record of 40.3 degrees Celsius on Monday, the Japan Meteorological Agency said.

Toyama city in Toyama prefecture, also in the central region, hit 39.8 degrees, the highest temperature since records began.

Fifteen other locations across cities and towns soared to new highs between 35.7 and 39.8 degrees, added the agency, which monitors temperatures at more than 900 points in Japan.

On July 30, Japan experienced its highest recorded temperature, a sizzling 41.2 degrees in the western region of Hyogo.

The rainy season ended about three weeks earlier than usual in western regions of Japan, another record.

With low levels of rainfall and heat, several dams in the northern region were almost empty, the land ministry said, with farmers worried that a water shortage and extreme heat could result in a poor harvest.

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.

Japan this year had its hottest June and July since data collection began in 1898, with the weather agency warning of further "severe heat" in the months ahead.

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. (AFP)