The number of dead from flooding and landslides has climbed to 175.
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Prime Minister Shinzo Abe visited flood-stricken parts of Japan on Wednesday as the death toll from the worst weather disaster in decades climbed to 176.
Dozens remain missing and there are health concerns amid scorching heat as well as fear of more floods.
Rescuers are combing through heaps of wood and thickly caked mud in a search for bodies, helped by sniffer dogs.
In some cases only the foundation of homes remained as they cut through debris with chain saws.
Torrential rain caused floods and triggered landslides in western Japan last week, bringing death and destruction to neighbourhoods built decades ago near steep mountain slopes
With temperatures of 33 degrees Celsius or higher in the devastated areas in Okayama and Hiroshima prefectures, attention turned to preventing heat-stroke among rescue workers and in evacuation centres where thousands of people have sought shelter.
Abe, who cancelled an overseas trip to deal with the disaster, was criticised after a photograph posted on Twitter showed Abe and his defence minister at a party with lawmakers just as the rains intensified.
After observing the damage from a helicopter flying over Okayama, one of the hardest-hit areas, Abe visited a crowded evacuation centre.
"We'll cut through all the bureaucracy to secure the goods people need for their lives, to improve life in the evacuation centres - such as air conditioners as the hot days continue -
and then secure temporary housing and the other things people need to rebuild their lives," he said.
Abe is up for re-election as party leader in September and has seen his popularity ratings edge back up after taking a hit over a cronyism scandal earlier this year.
His government pledged an initial 3.7 billion euros towards recovery on Tuesday, and a later special budget if needed.