Southwestern Japan was bracing for the effects of more torrential rain on Friday, on top of "unprecedented" downpours that swamped whole neighbourhoods, leaving at least 19 dead and eight missing.
Television footage showed torrents of muddy water carrying uprooted trees and other debris after Thursday's violent deluge, while rivers burst their banks and flooded towns and villages in the main southern island of Kyushu.
Reports showed residential streets in the city of Kumamoto covered in mud, while battered cars that had been swept away by flood water were left dumped on hillsides in scenes reminiscent of the March 2011 tsunami in the northeast.
In the city of Aso, landslides buried 17 households, killing at least 17 people with five more still missing.
Public broadcaster NHK showed rescuers continuing their search on Friday morning, using heavy machinery to remove uprooted trees, boulders and debris as rain fell.
The weather had eased somewhat by Friday morning, but the Japan Meteorological Agency forecast further downpours in Kyushu later in the day.
"We expect heavy rain on the same scale we saw yesterday will fall again today. We remain on the highest alert," said a local official in badly-hit Oita prefecture.
The city of Hita, Oita prefecture, issued evacuation orders to more than 11,000 people amid increasing fears the Kagetsugawa river, which runs through the city, would burst its banks, local officials said.
Nearly 25,000 people in other areas of the prefecture were advised to seek safety, the officials said.
In neighbouring Kumamoto prefecture, more than 250 households were told to evacuate, while everyone living in the floodplain of the Shirakawa river in Kumamoto city was advised to evacuate.
Friday's downpours were set to add to the misery for an area where 50,000 people were ordered to leave their homes on Thursday after it was lashed by the heaviest rainfall on record.
An official in Kumamoto prefecture said at least 18 people were known to have died, with troops and rescuers continuing their search for seven still missing.
In Oita, a man in his 70s died after being swept into a raging river, while another man remained missing.
Landslides and fallen trees have cut roads and water supplies in several places, with at least one small mountain community completely cut off, the local government said.
A Japanese military helicopter dropped packages of supplies including food and water onto the isolated district, it said.
The weather agency urged residents of Kyushu to continue exercising vigilance against mudslides and floods after rainfall of 10.1 centimetres (about 4 inches) per hour was recorded in the southern region of Kagoshima early Friday.
The weather agency forecast further about 20 centimetres of rainfall in the northern Kyushu region during the 24 hours to 6am on Saturday (2100 GMT Friday).