As heavy rains continue to wreak havoc on Japan's southwestern island of Kyushu, authorities have issued the highest-level warnings and ordered evacuations.

Authorities in Japan ordered thousands of people to leave their homes after landslides triggered by the region's "heaviest rain ever" killed at least one person and left three missing on Monday.

Japan's southwestern island of Kyushu saw torrential rains unleash landslides, prompting authorities in parts of Fukuoka and Oita prefectures to issue the highest-level warning for heavy rain.

A 77-year-old woman in Fukuoka Prefecture was killed when a landslide hit her home at night. In Saga Prefecture, three people were reported as missing after a landslide hit two homes, public broadcaster NHK reported.

The heavy downpour also forced suspension of the Shinkansen bullet train's service that runs between western Hiroshima and Fukuoka.

Japan on alert

Japan's Meteorological Agency (JMA) has urged people to leave their homes and take shelter as the heavy rains could unleash floods and more landslides across the Fukuoka and Oita regions.

Non-mandatory orders were issued for evacuation in parts of Fukuoka, Oita and adjoining prefectures.

"A special heavy rain warning has been issued for municipalities in Fukuoka Prefecture. This is the heaviest rain ever experienced" in the region, Satoshi Sugimoto of the JMA said.

Kyushu prepares for disaster

It is expected that northern regions in Kyushu will receive additional rainfall of up to 200 millimeters (7.87 inches) in the next 24 hours, Sugimoto said.

"There is a very high possibility that some kind of disaster has already occurred... The situation is such that lives are in danger and safety must be secured," he added.

A taskforce has been constituted to oversee and coordinate the appropriate disaster response, according to the prime minister's office.

Japan is currently witnessing its annual rainy season wherein it often sees heavy rainfall that sometimes leads to floods and landslides.