Rescue workers waded through muddy, waist-high waters on Monday searching for missing people after one of the worst typhoons to hit Japan in recent history, with rain forecast to resume later in the day.
Prime Minister Shinzo Abe said vast areas had been struck by the storm and called for urgent support to the affected.
At least 40 people were killed in the typhoon that left vast sections of towns in central and eastern Japan under water, with another 16 missing and 189 injured, public broadcaster NHK said.
"There still are many residents who have yet to be accounted for. Our people in uniform are working day and night in search and rescue operations," Mr Abe told an emergency meeting of ministers.
"Damage has been made in an extremely wide range of areas, and more than 30,000 people are still being forced to remain in the state of evacuation. It is our urgent task to offer meticulous support to those who have been affected."
Typhoon Hagibis, which means "speed" in the Philippine language Tagalog, made landfall on Japan's main island of Honshu on Saturday and headed out to sea early on Sunday.
Groups of rescuers wearing goggles and snorkels searched for survivors while making their way in waist-high water in Nagano, central Japan, where the Chikuma River inundated a large area.
More than 110,000 police officers, fighter fighters, soldiers and coastguard personnel, as well as some 100 helicopters were mobilised for Monday's rescue operations, Chief Cabinet Secretary Yoshihide Suga said.
Later in the day, strong rain is forecast in some parts of central and eastern Japan, where soil is already loosened by record-breaking rain from the typhoon, prompting Mr Suga to urge residents to keep their guard up.
"Rain is expected in affected areas today. Because of the rain we have seen so far, levels of water are high in some rivers and soil is loose in some areas," Mr Suga said.
"Please remain on your guard for landslides and river overflows."
More than 92,000 households were still without power early on Monday, a national holiday, the Ministry of Economy, Trade and Industry said. That was down from 262,000 households as of midday on Sunday.