Japan is struggling to restore utilities after its worst weather disaster in 36 years killed 155 people, with survivors facing health risks from boiling temperatures and a lack of water.

Torrential rain unleashed floods and landslides in western Japan last week, bringing death and destruction. About 67 people are missing, the government said.

Power had been restored to all but 3,500 households but more than 200,000 people remain without water under scorching sun, with temperatures hitting 33 degress Celsius in some of the hardest-hit areas.

"There have been requests for setting up air conditioners due to rising temperatures above 30 degrees today, and at the same time we need to restore lifelines," Finance Minister Taro Aso said.

The government has set aside 70 billion yen ($US631 million) in infrastructure funds, with more in reserve.

Though the weather has cleared up, the disaster goes on.

A new evacuation order went out on Tuesday in a part of Hiroshima after a river blocked by debris overflowed its banks, affecting 23,000 people.

Another storm, Typhoon Maria, was bearing down on outlying islands in the Okinawa chain but it had weakened from a super-typhoon and was not expected to have any impact on Japan's four main islands.