More than one million people across the Japanese island of Kyushu have been ordered to evacuate, amid warnings of landslides and floods brought on by heavy rain.
Authorities urged residents in parts of Kagoshima and Miyazaki prefectures to move to safety immediately.
One elderly woman in Kagoshima city died after a mudslide hit her home.
Prime Minister Shinzo Abe has told residents of the cities to "take steps to protect their lives".
Kagoshima prefecture has asked Japan's self-defence forces to help with the relief efforts, Governor Satoshi Mitazono reportedly said.
The entire populations of Kagoshima city, Kirishima and Aira were ordered to leave. Another 930,000 people in the south of the island were also advised to move.
But by 1600 local time (0700 GMT), the country's Fire and Disaster Management Agency reportedly said fewer than 4,000 people had been evacuated.
Weather officials say 1,000mm (39in) of rain has fallen on Kyushu island since Friday, and Japan's Meteorological Agency forecasts the rains will continue into next week.
A further 350mm of rain is expected in the southern part of the island and 300mm in the northern part by Thursday morning, with some areas predicted to get more than 80mm of rain every hour. The agency said a month's rainfall could hit parts of Kyushu in just 24 hours.
The island of Shikoku is also forecast to receive up to 250mm of rain in the same period. The rainy front is expected to hang over the entire Japanese archipelago until Saturday.
Last July about 200 people died in western Japan in the country's worst flooding disaster in decades. It was the highest death toll caused by rainfall in Japan since 1982.
About two million people were evacuated and more than 70,000 emergency workers were deployed after the heavy rain caused floods and landslides in the region.