Troops Sunday airlifted supplies to thousands of people cut off by landslides and torrential downpours that have killed at least 24 in southwest Japan as meteorologists warned of further heavy rain.

Television footage showed soldiers loading food, water and medical supplies onto military helicopters to send them to mountainous areas in Yame, Fukuoka prefecture on Kyushu island.

Local authorities were separately dispatching rescue helicopters to take patients and elderly villagers to hospital from the isolated area, where at least one person was killed, officials said.

Some 2,000 people regained access but 3,500 others remained cut off since Saturday as landslides and fallen trees have blocked roads and water supplies in the region which has been hit by unprecedented rainfall since Wednesday.

"It is still uncertain when we can remove rubble from the roads so that the remaining people can secure access," said Machiko Koga, a spokeswoman for Yame City government.

Rescue operations continued in other affected areas of Kyushu, where at least eight people were still missing after a total of 24 people were confirmed dead in landslides or floods, officials said.

Public broadcaster NHK showed rescuers using heavy machinery to remove uprooted trees, boulders and debris, while residents scooped mud out of their houses with shovels.

Some 3,600 people remained ordered or advised to leave their homes as at least 2,800 houses were flooded, NHK said, after local authorities lifted similar advice to some 400,000 others by Sunday morning.

The weather eased somewhat Sunday bringing temporary relief, but the Japan Meteorological Agency warned of more heavy rain, landslides and floods on the main southern island of Kyushu.

"A peak of heavy rain in northern Kyushu has passed, but there is fear that driving rain with thunder may hit northern Kyushu as warm and humid air is flowing to the rain front," the agency said.

"Please be vigilant of damage from landslides and floods as part of the ground has already softened and water is still overflowing from rivers because of record rainfalls," it said.

Rainfall of up to 81.7 centimetres (32.2 inches) has been recorded in hardest-hit Aso, situated at the foot of a volcano, where at least 18 people were killed and four others were still missing.

Television footage showed torrents of muddy, debris-strewn water and flooded houses following what officials described as "unprecedented" downpours from a seasonal rain front.

Heavy rainfall was also monitored in Kyoto, some 500 kilometres (310 miles) east of the affected areas in Kyushu, on Sunday, flooding more than 20 houses, news reports said.

About 20 people were temporarily trapped in the city as stream broke a river bank following rainfall of nine centimetres per hour, but they were later rescued safely, the reports added.