A huge rescue operation is under way in central Japan after a landslide hit the popular resort of Atami, killing two people and leaving 20 others missing.

Hundreds of rescuers began sweeping the hillside for survivors early on Sunday after a torrent of black mud crashed through the city a day earlier.

Several houses were swept away by the mudslide, which followed heavy rain.

Atami has had more rainfall in the first three days of July than it usually sees in the whole month.

Video posted on social media on Saturday showed mud plummeting down a mountain in the prefecture of Shizuoka, weaving through the city of Atami towards the sea.

A resident said he heard a "horrible sound" and fled as the landslide engulfed everything in its path.

"We are trying our best to search for survivors as quickly as possible while carrying out the operation very carefully as it is still raining," a local official told AFP news agency.

The weather has been similar in neighbouring Kanagawa prefecture.

Japan is a very mountainous and densely populated country and landslides are not unusual, says the BBC's Rupert Wingfield-Hayes in Tokyo.

But there is growing evidence that climate change is making these sorts of extreme weather events more frequent and more destructive, our correspondent adds.

The mudslide struck at 10:30 local time on Saturday (01:30 GMT), according to a local resident.

One witness told national broadcaster NHK: "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."

Another resident, Chieko Oki, told AFP: "The big electricity pylons here were shaking all over the place and no sooner had I wondered what was going on than the mudslides were already there."

One man could only escape by climbing a ladder.

"The mudslide came really close, right in front of my house. I could hear it coming before I saw it. I couldn't get away, so I climbed up a ladder," he told NHK.

Another man described hearing an "unimaginable sound". "I knew it was a landslide. It's been raining constantly for three days, it's been steady rather than a sudden downpour," he said.

Landslide cuts through Japanese city

Prime Minister Yoshihide Suga has put together a taskforce to respond to the disaster and the wider emergency caused by heavy rainfall on the Pacific coastline. He asked people in the area to remain on alert.

Police, firefighters and members of Japan's military are involved in a search operation.

Atami's Mayor Sakae Saito told local media that up to 300 homes had been affected by the landslide.

Meanwhile, hundreds of thousands of residents in three prefectures - Shizuoka, Kanagawa and Chiba - have been ordered to evacuate following warnings of further flooding in low-lying areas.

Last July dozens were killed in flooding. More than 200 died in 2018 when parts of western Japan were inundated.