TOKYO — Torrential rain pounding southwestern Japan triggered a mudslide early Friday that swallowed four people and was threatening to cause flooding and more landslides in the region.

The mudslide in the city of Unzen in Nagasaki prefecture hit two houses with four residents total. A woman in her 50s was pronounced dead, while a man in his 60s was seriously injured, according to Unzen city officials. Rescue workers were searching for the two other residents.

The Japan Meteorological Agency issued heavy rain and mudslide warnings in parts of the southern main island of Kyushu. Earlier warnings for Hiroshima in western Japan, where record rainfall fell earlier this week, were downgraded as rains subsided, AP reported.

The meteorological agency added that the rain front could stay over the country for about a week.

The meteorological agency said nearly 500 millimeters (20 inches) of rain fell in parts of Nagasaki in the past 48 hours, exceeding the average for the month of August. More downpours were forecast.

Japan on Friday issued the most serious level 5 risk alerts in the western prefecture of Hiroshima, citing unprecedented rains in the region and imminent risk of floods and other disasters.

On Thursday, hundreds of thousands of residents of Nagasaki and other parts of Kyushu island in southwest Japan were asked to evacuate to avoid floods and the risk of landslides caused by torrential rain.

Japanese Prime Minister Yoshihide Suga's office set up a disaster control center on Friday to handle potential disasters. "Torrential rains could continue in regions around western Japan," Suga said.

Heavy rains continued to lash western Japan and other areas intermittently on Thursday due to a stationary front near the Tsushima Strait becoming active.

The northern Kyushu region and nearby Yamaguchi Prefecture are feared to receive localized torrential rain of 50 to 60 millimeters per hour through Friday. The Japan Meteorological Agency (JMA) is calling for people to be on their guard against landslides, inundations and river flooding.

According to the agency, the amount of rainfall from the onset of precipitation until 10 a.m. on Aug. 12 reached 234.5 millimeters in Satsuma, Kagoshima Prefecture, 216.5 mm in Ebino, Miyazaki Prefecture, 215.5 mm in Fukuoka's Sawara Ward, 210 millimeters in the city of Nagasaki, and 208.5 mm in Shimabara, Nagasaki Prefecture.

The maximum rainfall forecast over the 24-hour period up to 6 a.m. on Aug. 13 is 300 mm in the northern Kyushu region, 250 mm in southern Kyushu, 200 mm in the Shikoku region in western Japan, 180 mm in the Kinki region also in the west, and 120 mm in the Chugoku region in the west and the Tokai region in central Japan, respectively.

Heavy rain is likely to continue hitting many areas from Saturday onwards. The maximum rainfall projected for the 24-hour period up to 6 a.m. on Saturday is between 200 and 300 mm in Kyushu, Shikoku, Kinki and Tokai, as well as in the Kanto-Koshin region that includes the greater Tokyo area. — Agencies