The Japanese government says at least 100 people have died or are presumed dead from the heavy rains, floods and mudslides that have struck western Japan, The Associated Press reported.
Chief Cabinet Secretary Yoshihide Suga told a news conference Monday that 68 people were unaccounted for, many of them in the hardest-hit Hiroshima area.
Suga said 87 people were confirmed dead and 13 others had no vital signs when they were found as of early Monday.
Searches and cleanup efforts were taking place in the southwestern region where several days of heavy rainfall set off flooding and landslides in a widespread area.
Dozens of people have been killed and more than two million forced to flee their homes after unprecedented rains pounded southwest Japan, The New Daily reported.
Japanese broadcaster NHK reports authorities saying at least 85 people are dead and another six are in critical condition, after widespread flooding and deadly mudslides swept the country.
The western Japanese city of Kurashiki has been hit hardest by the torrential rains, with 1000 people stranded and 100 in hospital, after the country experienced three times the usual precipitation for a normal July.
Around 364mm, approximately 1.5 times its monthly average rainfall between 5am and 7am local time in Uwajima, while 263mm fell in Sukumo City in the same two-hour period, NHK said.
In all, four million people have been advised to evacuate from eight prefectures, including Kyoto and Hiroshima.
"The record rainfalls in various parts of the country have caused rivers to burst their banks, and triggered large scale floods and landslides in several areas,” Cabinet Secretary Yoshihide Suga said Sunday night.
Television footage showed people, apparently patients and staff, waiting to be rescued on a balcony at Mabi Memorial Hospital, while many cars floated in muddy water and a person was rescued by helicopter from an elderly care facility.
The overall death toll from the rains in Japan rose to at least 85 on 2am Monday morning (AEST) from 66 on Sunday.
Another 60 were missing, NHK said, and more rain was set to hit some areas for at least another day.
The rain set off landslides and flooded rivers, trapping many people in their houses or on rooftops.
"We’ve never experienced this kind of rain before,” an official at the Japanese Meteorological Agency (JMA) told a news conference. "This is a situation of extreme danger.”
Among the missing was a nine-year-old boy believed trapped in his house by a landslide that killed at least three others, including a man in his 80s.
"All I have is what I’m wearing,” a rescued woman clutching a toy poodle told NHK. "We had fled to the second floor but then the water rose more, so we went up to the third floor.”
Japan’s government set up an emergency management centre at the prime minister’s office and some 54,000 rescuers from the military, police and fire departments were dispatched across a wide swath of southwestern and western Japan.
"There are still many people missing and others in need of help, we are working against time,” Prime Minister Shinzo Abe said.
Emergency warnings for severe rain remained in effect for three prefectures, with 300mm predicted to fall by Monday morning in parts of the smallest main island of Shikoku.
Evacuation orders remained in place for some 2 million people and another 2.3 million were advised to evacuate, although rain had stopped and floodwaters receded in some areas. Landslide warnings were issued in more than a quarter of Japan’s prefectures.