Torrential rain hit Japan's southwestern island of Kyushu on Monday, with at least one more river bursting its banks, as the death toll from three days of floods and mudslides rose to 44, including 14 at an old people's home.

Evacuation orders were issued for more than half a million island residents, as well as evacuation advisories for tens of thousands more in western Japan, broadcaster NHK said.

Prime Minister Shinzo Abe said the rain was forecast to head east by Wednesday and ordered round-the-clock search and rescue operations. Ten people were missing, NHK said.

TV pictures showed streets turned into rivers rushing by at waist high, a collapsed bridge, upturned cars and a helicopter winching a man to safety from an inundated house.

The old people's home was flooded in the island's central prefecture of Kumamoto. NHK did not give details.

"I urge all citizens to carefully follow the information provided by local authorities and stay alert to take actions to protect their own lives," Abe said at the start of a government task force meeting.

Chief Cabinet Secretary Yoshihide Suga said 40,000 members of the Self-Defence Force were involved in rescue missions.

He added that evacuation centers were also working on preventing the spread of the coronavirus by distributing disinfectant and asking evacuees to self-distance.

The floods are Japan's worst natural disaster since Typhoon Hagibis killed about 90 people in October.