Rain-sodden slopes collapsed in torrents of mud, rock and debris early Wednesday in the outskirts of Hiroshima, killing at least 10 people and leaving 22 missing, the government said.
Video footage from the national broadcaster NHK showed rescue workers suspended by ropes from police helicopters pulling victims from the rubble. Others gingerly climbed into windows as they searched for survivors in crushed homes.
Hillsides caved in or were swept down into residential areas in least five valleys in the suburbs of the western Japanese city after heavy rains left slopes unstable.
The Fire and Disaster Management Agency, citing the local government, said 10 people were confirmed dead and another 22 were missing as of mid-afternoon. It said 19 people were injured, two seriously.
"A few people were washed away and it is hard to know exactly how many are unaccounted for," said local government official Nakatoshi Okamoto, noting that the conditions in the disaster area were hindering efforts to account for all those affected.
Authorities issued warnings that further rains could trigger more landslides and flooding.
Landslides are a constant risk in mountainous, crowded Japan, where many homes are built on or near steep slopes. Torrential rains in the early morning apparently caused slopes to collapse in an area where many of the buildings were newly constructed.
Damage from land and mudslides has increased over the past few decades due to more frequent heavy rains, despite extensive work on stabilizing slopes. In the past decade there have been nearly 1,200 landslides a year, according to the land ministry, up from an average of about 770 a year in the previous decade.
In October last year, multiple mudslides on Izu-Oshima, an island south of Tokyo, killed 35 people, four of whose bodies were never recovered. Those slides followed a typhoon that dumped a record 824 millimeters of rain in a single day.