Rescue teams trawled Monday through muddy debris in a landslide-hit Japanese holiday town looking for survivors, as concerns grew that dozens of people may be missing.

Soldiers and emergency workers used hand-held poles and mechanical diggers in the desperate search, two days after a torrent of earth slammed down a mountainside and through part of the hot-spring resort of Atami in central Japan.

Three people have been confirmed dead, although authorities are struggling to pinpoint the whereabouts of dozens of residents as they scour the wreckage of 130 hillside homes and other buildings that were destroyed.

Vehicles were buried and buildings tipped from their foundations in the disaster, with an air-conditioning unit seen dangling from one devastated home towards the slurry below. "We have confirmed that 102 people are safe and we are still checking the safety of other 113 people, out of 215 residents who are believed to have been around the landslide-hit area," town official Yuki Sugiyama told AFP.

Authorities had initially said just 20 people were missing, but Atami mayor Sakae Saito said Sunday evening that was only an estimate based on an early assessment.

Prime Minister Yoshihide Suga confirmed on Monday authorities had yet to determine how many people were unaccounted for, while the focus was still on finding survivors.

"The national government, together with municipal governments, will verify (how many) are missing," Suga said. "(Rescue workers) are doing their best to rescue as many people as possible, as soon as possible", he added.

The landslide occurred during Japan's annual rainy season, and followed days of intense downpours in and around Atami.

Rescuers on Monday took advantage of a break in the rain to continue their search, wading through streams of murky water and moving blocks of timber and other debris out of the way. Non-compulsory evacuation orders have been issued to more than 35,700 people across Japan, mostly in the Shizuoka region including Atami, which is around 90 kilometres (55 miles) southwest of Tokyo.

The weather agency forecast heavy rain in the wider region, warning that more landslides could take place.

Atami reportedly recorded more rainfall in 48 hours than it usually does for the whole of July, and survivors told local media they had never experienced such strong rain in their lives.

Scientists say climate change is intensifying Japan's rainy season because a warmer atmosphere holds more water.

Survivors at a nearby evacuation centre told AFP on Sunday of their panic when the landslide began. "When I opened the door, everyone was rushing into the street and a policeman came up to me and said: 'What are you doing here, you have to hurry, everyone is evacuating!'" local resident Kazuyo Yamada told AFP. "So I went out in the rain in a hurry, without changing, with just a bag."