Military helicopters have plucked residents from the top floors of their homes after floodwaters inundated a city north of Tokyo.
As heavy rain pummelled Japan for a second day, the Kinugawa River broke through a flood embankment, sending a wall of water into Joso, about 30 miles north east of the capital.
National broadcaster NHK showed aerial footage of rescuers being lowered from helicopters and clambering on to second-floor balconies to reach stranded residents.
Entire homes and cars were carried away on the torrent as the Kinugawa River burst its banks after two days of heavy rainfall.
One rescuer descended four times over a 20-minute period to take four people up one by one, as a deluge of water swept around the home.
Others waved cloths from their homes as torrents of water around them washed away cars and knocked buildings off their foundations.
The chief forecaster at the Japan Meteorological Agency (JMA), Takuya Deshimaru, said that the rainfall was “unprecedented” for that part of Japan.
“We can say this is an abnormal situation and there is imminent serious danger,” he said.
The hardest-hit areas have been Ibaraki and Tochigi prefectures. Japan’s Meteorological Agency had put both regions on its highest level of alert.
Saori Mori, who lives close to the Tone River in the town of Abiko, said “the water is right up to the top of the banks now”.
“We have been told to pack and prepare to evacuate as soon as we are told to,” Ms Mori said, adding that she and her family were “getting ready for a fast exit”.
Elsewhere in the region, one woman was missing hours after a landslide hit houses at the foot of a steep, wooded incline. Bullet train services were partially suspended.
Tokyo was also drenched with rain, but the hardest-hit area was to the north in Ibaraki and Tochigi prefectures.
The rain came on the heels of Tropical Storm Etau, which caused similar flooding and landslides on Wednesday as it crossed central Japan.
The Fire and Disaster and Management Agency said 15 people were injured by Etau, two seriously - both elderly women who were knocked over by strong winds.
Japan’s Kyodo news service reported that 39 people had been rescued by Japan’s Self-Defence Forces and rescue work was continuing. Akira Motokawa, a city evacuation official, told NHK that rescuers had been unable to respond to the volume of calls for help.
The Transport Ministry estimated that 6,900 households had been affected by the flooding, Kyodo said, adding only about 2,500 of the city’s residents had been evacuated to shelters. The floodwaters reached at least five miles from the breached embankment.
Many other areas of eastern and north-eastern Japan have also been issued weather warnings, including Fukushima prefecture, home to the still-damaged nuclear plant hit in 2011’s earthquake and tsunami.