Two bodies were found after a huge landslide at a resort town in central Japan swept away homes on Saturday following days of heavy rain, with around 20 people still missing, officials said.

Television footage showed a torrent of mud obliterating buildings as it crashed down a hillside in Atami, southwest of Tokyo, sending people fleeing as it buried part of a road.

"I heard a horrible sound and saw a mudslide flowing downwards as rescue workers were urging people to evacuate. So I ran to higher ground," the head of a temple near the disaster told public broadcaster NHK.

Much of Japan is currently in its rainy season, which often causes floods and landslides
Much of Japan is currently in its rainy season, which often causes floods and landslides AFP / Adrian DENNIS

"When I returned, houses and cars that were in front of the temple were gone."

Prime Minister Yoshihide Suga said emergency services and the military had launched rescue and evacuation missions, warning that more downpours were forecast.

"There is a possibility of heavy rain due to the rain front, so we still need to be alert at the maximum level," he said at an emergency disaster meeting.

Atami saw rainfall of 313 millimetres in just 48 hours to Saturday -- higher than the average monthly total for July of 242.5 millimetres, according to NHK.

Emergency services and the military have launched rescue and evacuation missions
Emergency services and the military have launched rescue and evacuation missions JIJI PRESS / Handout

Two people were "found in a state of cardio and respiratory arrest", the regional governor said, an expression often used in Japan before confirming death.

"Because of the heavy rain, the ground loosened and the mudslide occurred... it picked up speed and swept away houses together with people," Shizuoka Governor Heita Kawakatsu told reporters.

He said "around 20" people were still missing after being swept away by the landslide.

The disaster began at around 10:30am at a river near the city
The disaster began at around 10:30am at a river near the city JIJI PRESS / Handout

The disaster began at around 10:30 am at a river near the city, which is around 90 kilometres (55 miles) from Tokyo and is famous as a hot spring resort.

A video posted on TikTok from the scene showed a huge slurry of mud and debris sliding slowly down a steep road and nearly engulfing a white car, which drove away before a faster and more violent torrent arrived.

In other clips on social media, the landslide was seen toppling electricity poles, with large areas left inundated by several waves of earth.

Much of Japan is currently in its annual rainy season, which lasts several weeks and often causes floods and landslides, prompting local authorities to issue evacuation orders.

Scientists say climate change is intensifying the phenomenon because a warmer atmosphere holds more water, resulting in more intense rainfall.

More than 200 people died as devastating floods inundated western Japan in 2018.

The highest evacuation alert, which urges people "to secure safety urgently", has been issued to Atami city which has more than 20,000 households, according to NHK.

Residents in many other cities in Shizuoka have also been ordered to evacuate.

Around 2,800 homes in Atami have been left without power, according to the Tokyo Electric Power Company.

Shinkansen bullet trains between Tokyo and Osaka were temporarily stopped due to the heavy rain, while other local trains in rain-affected areas were also halted, rail company websites said.