Two people died in southern Japan on Saturday after heavy rain overnight caused floods and mudslides, according to official sources.
More than a dozen people are missing, and many others are stranded on rooftops waiting to be rescued.
In the prefectures of Kumamoto and Kagoshima, authorities have urged more than 75,000 residents to evacuate.
Footage from local broadcaster NHK showed large areas of Hitoyoshi town in Kumamoto covered with muddy waters from the Kuma River.
The water level has reached car windows and houses are partly submerged.
Prime Minister Shinzo Abe has set up a task force to respond to the situation and the rescue of those missing.