Torrential rain hit the main island of Kyushu in southwestern Japan on Wednesday, causing river floods and mudslides and leaving at least 10 people in Fukuoka and Oita prefectures reportedly unaccounted for.

Some houses are feared washed away and dozens of people are stranded while over 430,000 people were ordered to evacuate their homes and seek shelter in the affected area, including more than 300,000 people in Fukuoka's Kurume.

Six of the people unaccounted for include a child and are feared to have been washed away or buried alive, according to Fukuoka police. They also include a man in his 70s missing in Asakura, Fukuoka, the city government said.

Separately, three prefectural workers from an office in Asakura lost contact during patrol, the Fukuoka prefectural government said. The 10th person reportedly unaccounted for is a man in Hita, Oita, according to the Hita municipal government.

Asakura has been one of the hardest hit by Wednesday's floods, with precipitation reaching a record 515 millimeters over a 24-hour period through late Wednesday. Asakura city issued evacuation orders for 54,000 residents.

The Japan Meteorological Agency urged "utmost vigilance" in wide areas of Fukuoka and neighboring Oita, saying the heavy rain could bring a once-in-decades disaster.

The rain disrupted traffic, with an overflowing river washing away a railway bridge in Hita, severing the JR Kyudai Line, which connects Kurume and Oita city, according to the transport ministry. Other bridges have also been lost in the city. The Oita Expressway was partially closed due to the rain.

The rain also left up to 6,400 households in Fukuoka and Oita without power.

The municipal government in Asakura asked the Self-Defense Forces for help as around 50 people were stranded at an elementary school in a flooded area. The Fukuoka and Oita prefectural governments also called for SDF dispatches.

In Tokyo, Prime Minister Shinzo Abe instructed the government to make utmost efforts to ascertain the degree of damage and rescue people needing help. Some 6,000 personnel, made up of firefighters, police officers and SDF members, are expected to engage in rescue, search and recovery efforts from Thursday morning, according to the government.

"A river has overflowed and houses are flooded, I don't know where the river or a road is," said Hiromichi Hayashi, a delivery company operator in Asakura. The 61-year-old man said an acquaintance was almost buried by a mudslide.

Heavy rain could hit a wider part of western Japan through Thursday, the weather agency warned.

Aside from Asakura, particularly strong rain was observed in Tosu in neighboring Saga Prefecture and Hita in Oita, with per-hour rainfall hitting around 110 to 120 mm.

In Hita, the Ohi River flooded, leaving at least five people isolated while in Nakatsu in Oita, a major road was blocked by a fallen tree. In Fukuoka's Toho village, three houses were reportedly washed away, Chief Cabinet Secretary Yoshihide Suga said at a hastily called news conference.

Heavy rain also hit other parts of western Japan on Wednesday. A man's body was found in a river in Hiroshima and local police believe he was swept away as the river level rose due to the torrential rain that pummeled Shimane and Hiroshima prefectures.

The Shimane government urged 20,000 residents in 9,200 households to evacuate their homes.

The rain caused some schools in Shimane to cancel classes Wednesday and disrupted some train services in the two prefectures.

The city of Hamada in Shimane facing the Sea of Japan saw hourly precipitation of over 80 mm Wednesday morning as a seasonal rain front brought in wet air from the East China Sea, causing a strip of storm clouds to develop, the Japan Meteorological Agency said.