The death toll from flooding and mudslides caused by heavy rain on the Japanese southwestern island of Kyushu rose to 16 on Saturday, while at least 20 people remained unaccounted for as rescue efforts continued in a race against time.

Authorities also found several people showing no vital signs in Fukuoka Prefecture, which was devastated along with neighboring Oita Prefecture by the torrential rain.

Rescue workers are continuing efforts to save people, even as the first 72 hours of the disaster, considered a crucial period for finding survivors, have lapsed.

The Japan Meteorological Agency warned residents to remain alert to mudslides and other disasters because heavy rain may fall through Saturday following Wednesday's downpour.

In Saga Prefecture, five bodies were discovered in the Ariake Sea, surrounded by Kumamoto and other prefectures and situated several tens of kilometers from the disaster-stricken areas.

GALLERY: Torrential rain batters southwestern Japan

VIDEO: Drone footage shows extent of flooding in Kyushu

Prefectural police are investigating a possible link to the torrential rain. Since areas along the Chikugo River flowing into the sea include those hit hard by the heavy rain, the bodies may have been washed downstream.

In Fukuoka, more than 20 people were unaccounted for, while Oita's initially reported missing are now accounted for, according to their local governments.

Chief Cabinet Secretary Yoshihide Suga told reporters the same day that a total of 1,022 people have been rescued so far after the government dispatched 12,000 Self-Defense Force members, police officers and firefighters to the disaster-hit area.

While access to stranded residents in isolated areas in Asakura city and the village of Toho, both in Fukuoka, was mainly restored, 545 people remained stranded in Oita's Hita.

In Asakura, one of the areas hit hardest by the torrential rain, work to remove mud and uprooted trees which severed road access has continued, helping to reconnect most of the isolated areas.

Blocked sections on the Kyushu Expressway have all been cleared as well, according to West Nippon Expressway Co.

Among the victims, three bodies found Friday in Asakura have been identified as Yukari Eto, 26, her 1-year-old son Yuya and Eto's 63-year-old mother Reiko Fuchigami, according to the local government.

Eto, who was pregnant, was holding her son in her arms when she was found underneath a collapsed house, according to a 66-year-old man who lived in the neighborhood, quoting a rescue worker who was at the site.

They were believed to have been visiting her parents' home in Asakura. The two-floor house was swept about 10 meters off its foundation and its first floor collapsed. The body of her mother was also found nearby, the neighbor said.

The man said he saw the father of Eto embracing their bodies. "I couldn't find anything to say to him," he said.

According to the meteorological agency, over 600 millimeters of rainfall were recorded in Asakura in the 72-hour period from Wednesday to Friday.