'A horrible sound': 20 missing following Japan landslide

At least two people have been killed in a landslide in Atami, southern Japan, after a week of torrential rain.

A torrent of mud and rock cascaded on to a road in Shizokua province, sweeping away nearby houses in the small town 90 kilometres south-west of Tokyo.

Twenty people are unaccounted for, Shizuoka Governor Heita Kawakatsu said on Saturday.

"Because of the heavy rain, the ground loosened and the mudslide occurred. It picked up speed and swept away houses together with people," he said.

Residents described the terrifying speed at which the disaster occurred.

"I heard a horrible sound and saw a mudslide flowing down as rescue workers were urging people to evacuate. So I ran to higher ground," one resident told Japanese national broadcaster NHK.

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

A Level 5 weather warning has been issued, the most severe, and Prime Minister Yoshihide Suga said the military would be sent to assist with recovery efforts.

"There may be more heavy rainfall and we need to be exercising the highest caution," Mr Suga said.

Japan is currently in the wet season, which can leave some communities vulnerable to flash floods. But in recent years, flash floods have become more intense, with about 200 people killed in the rainy season in 2018.

Some scientists say climate change plays a significant role in the worsening weather.

"The government is just starting to realise that it needs to take steps to mitigate the impact of global warming," Takashi Okuma, an expert in national disasters and a professor at Niigata University, told Reuters after the 2018 floods.

In the hours before Saturday's disaster, NHK reported that people were asked to leave their homes around the nearby areas of Tokyo, Shizuoka and Aichi.