Floodwaters have swamped a city near Tokyo, washing away houses and forcing dozens of people to rooftops where they had to be rescued by helicopters.
More than 30,000 people fled their homes and hundreds more were stranded by the water as heavy rain hit Japan for a second consecutive day.
The Kinugawa River broke through a flood embankment, sending water gushing into the eastern half of Joso, a city of 60,000 people about 30 miles north-east of Tokyo.
Aerial videos showed a wide swath of cityscape under water, more than one storey deep in some places. The rain follows tropical storm Etau, which caused flooding and landslides elsewhere on Wednesday as it crossed central Japan.
Japanese broadcasters showed live video of rescuers being lowered from helicopters and clambering onto second-floor balconies to reach stranded residents.
In one dramatic scene, a rescuer descended four times from a military helicopter over 20 minutes to lift up four people one by one.
Nearby, a man clung to a pole as the waters rose. He was taken up by a rescue worker who first had to be lowered into the rushing water so he could make his way over to the man.
Others waved from their roofs to get attention as torrents of water washed away cars and knocked over buildings. Photos from Japan's Kyodo News service showed people waiting for help on top of cars and a delivery truck.
By evening, muddy water was still rising on a street heading to Joso City Hall, and police were blocking traffic in that direction.
Akira Motokawa, a city evacuation official, told public broadcaster NHK that rescuers have been unable to keep up with the volume of calls for help.
A total of 176 people had requested help. Another 100 were reported trapped on the second floor of a flooded supermarket and 80 more in a nursing home.
More than 31,000 people in the affected 14 square mile area sheltered at schools, community centres and other safer areas. Military delivering food, blankets and water to about 780 people in communities who were stranded but not seeking rescue.
Dozens of residents had evacuated to City Hall. They rested in conference rooms and a waiting area on the first floor was opened for them to stay overnight.
Tokyo was drenched with rain, but the hardest-hit area was to the north in Ibaraki and Tochigi prefectures. One woman was missing hours after a landslide hit houses at the foot of a steep, wooded incline.
The Fire and Disaster and Management Agency said 22 people have been injured by the storms over the past two days, including three elderly women who were seriously hurt when strong winds knocked them over.