* 'Situation of extreme danger' -meteorological agency

* More rain expected in some areas

* Some 54,000 military, police dispatched

The overall death toll from the rains in Japan rose to at least 81 on Sunday after floodwaters forced several million people from their homes, media reports and the Fire and Disaster Management Agency said.

Another 58 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.

"This is a situation of extreme danger," an official at the Japanese Meteorological Agency (JMA) told a news conference.

A three-year-old girl whose home was hit by a landslide in Hiroshima prefecture was found dead by a search team.

"It's very painful," said one elderly man watching nearby. "I have a granddaughter the same age. If it were her, I wouldn't be able to stop crying."

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 western and southwestern Japan.

'SUDDEN DISASTER'

"There are still many people missing and others in need of help, we are working against time," Prime Minister Shinzo Abe said on Sunday morning.

Two sisters from an elementary school of just six pupils on the small island of Nuwa in Ehime prefecture were among the dead. The younger, a first-grader, was a star and the hope of the depopulated island, the principal told NHK.

"It was such a sudden disaster, I just cannot come to grips with it," the principal said.

Emergency warnings for severe rain in 11 prefectures - the most since a new warning system was introduced in 2013 - had been lifted by evening, but advisories for heavy rain and landslides remained in effect in many areas.

TV footage showed convenience stores with shelves mostly bare while elsewhere, residents lined up to receive water. Some 276,000 households were without water supply, Kyodo said.

Roads were closed and train services suspended in parts of western Japan while Shinkansen bullet train services resumed on a limited schedule after being suspended on Friday.

The rain began late last week as the remnants of a typhoon fed into a seasonal rainy front.

Automakers including Mazda Motor Corp and Daihatsu Motor Co suspended operations at several plants on Saturday and were to decide later on Sunday on plans for the coming week.

Electronics maker Panasonic Corp said one plant in Okayama, western Japan, could not be reached due to road closures, although it had been closed for the weekend anyway. A decision about next week would be made on Monday, it said.