Heavy rains across parts of Japan have left one person dead and at least one missing, according to authorities, as they issued evacuation warnings for nearly two million residents.

On Saturday, the country's weather agency warned of potential landslides, flooding and other disasters in western, central and eastern Japan, as a seasonal rain front triggered intense downpours.

In Yamaguchi prefecture, "a man was found dead" inside a car that had been washed into a river, a local police official told AFP.

And rescue workers in western Oita prefecture's Yufu were "still trying to make contact" with a 70-year-old man who lived in a home destroyed by a landslide, a city official said.

Non-compulsory evacuation orders were issued to about 1,855,000 residents in eight prefectures of western Japan including Oita and Yamaguchi, the Fire and Disaster Management Agency said in a statement.

Scientists say the climate crisis intensifies the risk of heavy rain in Japan and elsewhere because a warmer atmosphere holds more water.

Strong rains in 2021 triggered a devastating landslide in the central resort town of Atami that killed 27 people.

And in 2018, floods and landslides killed more than 200 people in western Japan during the country's annual rainy season.