At least 36 people are feared dead after record rains lashed areas of western Japan in the early hours of Saturday, causing rivers to break banks and flooding low-lying regions.
"Rescue workers are tirelessly continuing the search this morning," a spokesman for the western Kumamoto prefecture told AFP, with at least 11 people still unaccounted for.
Although the rain has subsided from its peak levels, the floods washed away roads and bridges, leaving many in isolated communities cut off.
Hirokazu Kosaki, a 75-year-old bus driver in the town of Ashikita, told Jiji press: "It was nothing but water as far as I could see."
In one of hardest-hit areas, residents spelled the words "rice, water, SOS" on the ground, while others waved towels and called for rescue and relief goods.
At a nursing home for the elderly, 14 people were feared dead when water from a nearby river inundated the ground floor, leaving those in wheelchairs unable to reach higher ground.
Emergency services, aided by locals in rafts, managed to rescue around 50 staff and residents from the facility, bringing them to safety by boat.
Heavy rain is expected to continue through Tuesday afternoon and the Japan Meteorological Agency issued a non-compulsory evacuation order for hundreds of thousands of residents in Kumamoto and neighbouring Kagoshima Prefecture.
Up to 250 millimeters of rain is expected in the 24-hour period through Tuesday morning in the southern part of Kyushu Island, which includes areas hit hard by the flooding, the agency said.
"It's such a mess," resident Hirotoshi Nishi told public broadcaster NHK as he swept debris from his mud-strewn front room.
"Many pieces of wood came into my house. I don't know what to do."
Evacuation efforts are being hampered by fears of spreading the coronavirus that has claimed almost 1,000 victims in Japan, with close to 20,000 cases.
Partitions have been set up at evacuation centres to keep distance between families and evacuees are made to wash their hands frequently, sanitise and wear face masks.
Local officials told AFP that 19 people had been confirmed dead from the floods while a further 17 were in a state of "cardio-respiratory arrest" -- a term often used in Japan before a doctor officially certifies death.
Some 4,640 homes in Kumamoto Prefecture remained without power as of Monday morning, according to Kyushu Electric Power Co.
Prime Minister Shinzo Abe said Sunday that more than 40,000 personnel from police and fire departments, the coast guard and Self-Defense troops would conduct search and rescue operations throughout the night.