The heaviest rainfall on record in Japan's southwestern island of Kyushu has left at least 20 people dead, 20 missing, and forced 50,000 people to evacuate, officials and reports said.
Thursday's reports came as emergency workers in Kumamoto prefecture responded to multiple reports of mudslides swallowing houses and people being trapped, with access roads blocked by mud or gushing water, officials said.
"Particularly in Kumamoto and Oita prefectures, we are seeing the heaviest rain that [the region] has ever experienced," the Japan Meteorological Agency said.
Troops have been deployed as almost 100mm of rain has fallen in a hour in some areas. Kumamoto experienced 50cm of rainfall in less than 24 hours.
The local government has received reports of at least 19 missing people, many of them swept away by swollen rivers or going missing after their homes were destroyed.
"Unfortunately, we believe the numbers [of dead and missing] will rise as we get more and more information from the field," a spokesman told the ADP news agency.
The national weather agency has said there is a risk of tornadoes as winds pick up and the weather gets worse.
"We may get more rain later and we are increasing our alert level for rivers overflowing," another official said.
In neighbouring Iota prefecture, a man in his seventies died after being swept into a raging river, while another man remained missing.
Yoshihiko Noda, the prime minister, promised full relief efforts to help affected residents.
"I have heard that this is a record for heavy rainfall. We will take effective measures," he said in a legislative session.
Self Defence Force troops have been deployed to the region for disaster relief efforts at the request of local governors.
In Kumamoto prefecture more than 17,000 households had been ordered to evacuate, with 5,000 more advised to seek shelter elsewhere.
Oita authorities issued evacuation orders to nearly 15,000 people and advised a further 10,000 to leave.
In all, more than 50,000 people in Oita and Kumamoto received evacuation orders, according to local media.