Japan's land ministry says an area of about 950 hectares, or 9.5 square kilometers, flooded in Nagano prefecture over the weekend. It was the result of heavy rainfall from Typhoon Hagibis that burst the banks of the Chikuma River.
In an aerial survey conducted by helicopter on Tuesday, ministry officials found the inundated zone stretches about 5 kilometers north to south along the river. It includes residential areas in Hoyasu and a bullet train depot in Akanuma, both in Nagano City.
The ministry has mobilized 23 pumper trucks to drain the water, with priority for areas with homes and community roads.
Officials say about 40 percent of the floodwater had been pumped out as of Monday afternoon.
In the adjacent Kanto region, officials estimate that about 4,000 hectares, or 40 square kilometers, were inundated after embankments collapsed along four rivers.
They say 20 pumper trucks are being used and most of the water has been drained from areas along the Naka River.