At least 100 people are thought to have died after record rainfall caused flooding and landslides in western Japan, a government spokesman says.
More than 50 others are believed to be missing, the Japan Times reported.
Since Thursday, parts of western Japan have received three times the usual rainfall for the whole of July. Two million people have been ordered to evacuate as rivers burst their banks.
"We've never experienced this kind of rain before," a weather official said.
Most of the deaths have occurred in Hiroshima prefecture.
Prime Minister Shinzo Abe said on Sunday that rescuers were "working against time".
"There are still many people missing and others in need of help," he told reporters.
In the town of Motoyama, on Shikoku island, 583mm (23in) of rain fell between Friday morning and Saturday morning.
Further rain warnings are in effect, with more than 250mm predicted to fall in some areas by Monday.