Rescue workers have found four more bodies in southern Japan, bringing the death toll from heavy rain to six with about 20 more missing, officials said.

Troops and rescuers gained access to some of the villages that were cut off by torrential rain and rescued more than a dozen stranded residents on Friday.

Chief Cabinet Secretary Yoshihide Suga said 12,000 troops and rescuers were focusing on remote villages where hundreds are still stranded.

The operation has been slowed by mud and floodwaters, and more flooding was forecast for the country's east.

"Heavy rain is forecast to continue intermittently," Suga said, while calling for continued vigilance.



"I would like people in the disaster zone to pay full attention to evacuation information," Suga added.

The four bodies were retrieved in Asakura town in Fukuoka prefecture, one of the hardest hit areas. One man was found on Thursday after he was covered by a mudslide and the three others, including a couple, were swept away by floodwater.

Heavy rain warnings are still in place for parts of the southern island of Kyushu after Typhoon Nanmadol swept across Japan earlier this week, dumping rain that has wrecked homes, roads and rice terraces.

Television footage showed rice fields and homes flooded after a river overflowed its banks. Roads and bridges were damaged and dozens of vehicles and houses destroyed and half covered with mud.

Residents from remote villages were being airlifted by military helicopters while soldiers waded through floodwaters carrying elderly residents on their backs.

Japan's Meteorological Agency said Fukuoka and Oita prefectures experienced unprecedented rainfall.

Amid search and rescue, Japan's royal family decided to postpone Saturday's formal announcement of Princess Mako's engagement with her college classmate out of consideration for the suffering of people in the affected areas, Japanese media reported.