At least two people died when a massive mudslide carrying debris crashed into rows of houses in a town west of Tokyo following heavy rains on Saturday, local media reported.
Officials said at least 19 people were still missing in the coastal town of Atami in Shizuoka prefecture, on the most populous island of Honshu.
Two women found in "cardiac and respiratory arrest" were later pronounced dead.
Six people have been rescued and are not in danger of death, the Japanese television station TBS reported.
Rescue operations are ongoing but have been hampered by adverse weather conditions.
Hundreds of homes damaged
The mudslide was estimated to be travelling at about 40 kilometers (25 miles) per hour, Professor Motoyuki Ushiyama of the Shizuoka University Centre for Integrated Research and Education of Natural Hazards told Kyodo news agency.
Ten houses were completely destroyed and up to 300 others damaged.
Yoshihide Suga, Japan's prime minister, has called a special emergency task force to respond to the crisis, broadcaster NHK reported.
TV footage, along with videos on social media, showed a black mudslide from the mountains crushing houses on the way.
A week of heavy rains
The mudslide came during an extended period of heavy rain across several parts of Japan.
Rains lashing the Shizuoka and Kanagawa prefecture has already exceeded the levels usually expected in July.
Experts cite climate change for the increased rainfall levels in Japan.
Officials in the Kanagawa, Shizuoka and Chiba prefectures have issued landslide and flood warnings.
mvb, am/mm (AP, Reuters, dpa)