Japanese weather officials are urging people in Yamagata Prefecture to ensure their safety after torrential rain caused the Mogami River to overflow.
The Meteorological Agency says unstable atmospheric conditions brought record-level rainfall to parts of the prefecture on Tuesday.
Rescue workers continue to search for missing people in Kumamoto Prefecture, southwestern Japan, after record rainfalls triggered floods and landslides over the weekend.
Officials say 24 people have been confirmed dead. A further 16 are without vital signs, and 12 others are missing.
Authorities in Kanagawa Prefecture, near Tokyo, say a nurse at a hospital in Sagamihara City has the new coronavirus.
They say Sagamihara Chuo Hospital is where a woman in her 80s, who was confirmed to have the virus after her death last week, was being treated earlier this month.