More heavy rains are expected through around Tuesday in the northern region of Tohoku, mainly on the Sea of Japan coasts of Yamagata and Akita prefectures.
Tohoku was hit by record rains as a seasonal rain front became active, and the downpours caused the Mogami and other rivers to overflow, submerging some areas and triggering landslides.
River levels remain high in Yamagata Prefecture, and the ground has loosened, mainly in northern Tohoku.
The seasonal rain front that stretched again over Tohoku on Saturday is causing rain clouds to develop over parts of Aomori and Miyagi prefectures, as well as southern Hokkaido.
Landslide alerts were issued in some parts of Miyagi.
Weather officials say localized torrential rain with lightning will likely hit Tohoku, and intermittent downpours are possible mainly in areas along the Sea of Japan coast through around Tuesday.
In the 24 hours through Sunday evening, up to 150 millimeters of rain is expected in the coastal areas of Tohoku along the Sea of Japan, and 120 millimeters in areas on the Pacific side of the region.
In the 24-hour period through Monday evening, up to 200 millimeters of rain is forecast for the Sea of Japan side and 150 millimeters on the Pacific side.
Weather officials say even a small amount of rain could heighten disaster risks in areas where riverbanks have been damaged or the ground has loosened.
People are advised to stay on the alert for overflowing rivers, flooding and landslides, and to secure their safety by, for example, evacuating before rain becomes heavy.