Search and rescue operations continued Thursday as torrential rain devastated Japan's southwestern main island of Kyushu, leaving six dead and at least four missing from flooding and mudslides.

The Japanese government dispatched about 7,800 personnel -- police officers, firefighters and members of the Self-Defense Forces -- to Fukuoka and Oita prefectures, where emergency warnings triggered by the downpour were lifted early Thursday afternoon.

The body of Tetsuo Fujimoto, 66, was discovered in Asakura, Fukuoka Prefecture, while in Hita, Oita Prefecture, two people were confirmed dead -- a 79-year-old man found in a river and Taketo Yamamoto, a 43-year-old male rescue worker engulfed by a mudslide.

Three other casualties were also later confirmed in Asakura.

GALLERY: Torrential rain batters southwestern Japan

According to the Fukuoka prefectural government, four people remained unaccounted for. In Oita Prefecture, 15 people could not be contacted.

"The government will do its utmost to save victims and take stock of the damage, placing priority on people's lives," Chief Cabinet Secretary Yoshihide Suga told a press conference, adding that it may consider expanding the scale of the rescue effort depending on the level of devastation.

The Japan Meteorological Agency had urged "utmost vigilance" in Fukuoka and Oita, saying a once-in-decades disaster was possible due to unstable atmospheric conditions.

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As of 10:30 a.m. Thursday, about 450,000 people from about 186,000 households had been ordered to evacuate to safer shelter. But in the two prefectures, at least 700 people were stranded due to damaged roads. The rain also disrupted rail services and left up to 6,300 homes without power in Fukuoka, Kumamoto and Oita prefectures on Thursday.

About 106,000 people in 39,000 households were still subject to evacuation orders as of Thursday afternoon.

Major mobile phone carriers NTT Docomo Inc., KDDI Corp. and SoftBank Group Corp. said Thursday that rainfall disrupted smartphone and mobile phone connections in some areas in northern Kyushu with no resumption in services in sight anytime soon.

"We have yet to grasp the whole picture of the damage," disaster management minister Jun Matsumoto told a ministerial meeting called Thursday in response to the disaster. He ordered rescue personnel to work closely with municipal governments to save lives.

In Asakura, hit hard by nearby flooded rivers, 54 people, including 18 pupils, were left stranded at an elementary school. About 1,700 homes were cut off from their water supply in the morning in the city, which saw record precipitation of 545.5 millimeters over a 24-hour period through 11:40 a.m. Thursday.

The number of people waiting to be rescued remains unknown but residents called for help on Twitter, with some posting photos or asking about the whereabouts of their family members.

Kyosuke Hosaka, a 65-year-old resident of Asakura, narrowly escaped muddy water that broke through the entrance of his home, shattering windows and washing away furniture.

"The water poured into my home with an awful destructive noise," he said, describing how the water reached chest level in a matter of seconds.

Hosaka escaped to higher ground by swimming and holding onto drifting objects. "It was really a near-death experience," he said.

Among those left stranded overnight in their homes in Asakura, Yuki Oyabu, 47, said, "We saw what was just like a river right in front of us. We could not even go to an evacuation center." The severity of the situation meant she was forced to stay at home with her two daughters.

A senior Asakura city official expressed concerns over the extent of the damage, saying, "The affected area is wide and the condition is much worse" than the heavy rainfall that hit Kyushu five years ago, leaving more than 30 people dead or missing.

The rain also hit western Japan and a 67-year-old man in Hiroshima Prefecture remains unaccounted for. It is feared he was swept away as he carried out a check on a water channel near his home, something he did every morning as a duty for the local community, police said.

The heavy rain was brought about by a swath of cumulonimbus clouds that stayed over the area in line with the movement of a seasonal rain front.

Rainfall of over 50 millimeters per hour was registered in some areas in Kyushu and further precipitation is expected through Friday, the weather agency said.