Two women were confirmed dead after torrents of mud crashed through a part of the hot-spring resort of Atami in central Japan on Saturday morning, following days of heavy downpours.
Nineteen people are rescued and around 20 others are still missing, the town's disaster-management spokesman Yuta Hara told AFP.
"We do our greatest to rescue survivors while carefully checking the weather and other conditions", he said.
Hara said around 130 homes and other buildings had been destroyed because the landslide swept through the residential district , leaving a quagmire that stretched right down to the nearby coast.
Vehicles were buried and buildings tipped from their foundations, with an air-conditioning unit seen dangling from one devastated home towards the slurry below.
Hara said the landslide was one kilometre (0.6 miles) long and 120 metres (400 feet) wide at some points.
Hundreds of rescue workers and military personnel were combing through the mud and debris with diggers and on foot, climbing across cracked roofs and sticking poles into the bottom to see for bodies.
TV footage showed coast guard divers searching in murky seas, while cops scoured damaged houses with sniffer dogs.
Rain hampered rescue operations however, with workers forced to abandon the location multiple times as smaller landslides happened and disaster warning alerts were issued.
Survivors at a close-by evacuation centre told AFP of their panic when the landslide began.
"When I opened the door, everyone was rushing into the road and a policeman came up to me and said: 'What are you doing here, you've got to hurry, most are evacuating!'" local resident Kazuyo Yamada told AFP.
"So I went call at the rain during a hurry, without changing, with just a bag".
Fisherman Hisao Shima, 58, said that when he heard the landslide warning siren, initially he "didn't think it had been getting to be that bad".
"But once I stepped outside later, the rumbling of the bottom all around was very strong", he said.
Atami, around 90 kilometres (55 miles) southwest of Tokyo, saw rainfall of 313 millimetres in only 48 hours to Saturday -- above the typical monthly total for July of 242.5 millimetres, consistent with public broadcaster NHK.
Much of Japan is currently in its annual season , which lasts several weeks and sometimes causes floods and landslides.
Scientists say global climate change is intensifying the phenomenon because a hotter atmosphere holds more water, leading to more intense rainfall.
More downpours are forecast within the coming days across Japan's main island.
"This rainy-season front is predicted to stay causing heavy rain in many areas. there's a fear that land disasters could occur even when the rain stops", Prime Minister Yoshihide Suga told ministers at an emergency meeting.
NHK said on Sunday that a minimum of seven other landslides had been reported across Japan.
"Landslides can occur again and again at an equivalent place albeit the rain stops. Residents and rescuers should remain on alert", Takeo Moriwaki, professor of geotechnical engineering at Hiroshima Institute of Technology, told AFP.
Town disaster spokesman Hara said 387 residents had been evacuated, with survivors in face masks seen reading newspapers with images of the disaster on the front page.
Residents in many other cities in Shizuoka have also been ordered to evacuate.
