Two people died and about 20 others remain missing after torrential rain triggered a large mudslide southwest of Tokyo on Saturday, destroying more than 10 houses, local authorities said.

A video posted on Twitter showed black water mixed with soil and sand flowing rapidly from the top of a mountain — making a rumbling sound — at about 10:30 a.m. in Atami, Shizuoka Prefecture.

“I’ve lived here for about 60 years but this is my first (such) experience,” said 70-year-old Masaru Isei, who lives about 50 meters from where the mudslide occurred.

Isei heard what sounded like heavy rain at around 10:45 a.m. When he opened a window on the second floor of his house he saw that his storage shed had been swept away and that a car in the parking lot was sinking into the ground. He then evacuated with his wife to an acquaintance’s house located on higher ground, taking only his smartphone and wallet.

An 84-year-old man first noticed a rotting smell. When he looked upstream of a nearby river, he saw a huge amount of soil and sand about 5 meters high moving toward him.

The river, usually less than 2 meters wide, was overflowing with the mixture and had swollen to several dozen meters wide, he said.

The speed of the mudslide is estimated to have been around 40 kilometers per hour, said Motoyuki Ushiyama, a professor at the Shizuoka University Center for Integrated Research and Education of Natural Hazards.

The site is in a sediment disaster warning area, Ushiyama said. It had been raining heavily in Shizuoka for some time.

Fumitoshi Imaizumi, a professor of erosion control engineering at Shizuoka University, said the area is prone to mudslides due to volcanic sediment accumulating on slopes.

“The total amount of rainfall in the area was quite heavy, so it created conditions for (mudslides) to occur.”

About 200 homes had been left without power, an Atami city official said. The mudslide reached the nearby coast, according to police.

“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,” a leader of a temple near the disaster told NHK.

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

Around 21,000 households in Atami, home to hot spring resorts, were ordered to ensure their safety immediately as the city government issued the highest level of evacuation alert.

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

Rescue workers are searching for those who remain missing. They also received about 10 calls from people who are trapped in their houses due to the mudslide.

The Ground Self-Defense Force dispatched around 30 members to the area in response to a request from the prefectural government.

Prime Minister Yoshihide Suga called an emergency meeting with members of his Cabinet in the evening, instructing them to work with local authorities to ascertain the scope of the damage and calling on the public to be ready to evacuate when necessary and “take action to protect your lives.”

The government has set up a task force at the Prime Minister’s Office to collect information as heavy rainfall continued to lash areas along the Pacific coast in central and eastern Japan.

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

Water levels on the Kise River in Numazu, Shizuoka Prefecture, surged on Saturday after heavy rains hit the area. | NUMAZU OFFICE OF RIVERS AND NATIONAL HIGHWAYS / VIA KYODO
Water levels on the Kise River in Numazu, Shizuoka Prefecture, surged on Saturday after heavy rains hit the area. | NUMAZU OFFICE OF RIVERS AND NATIONAL HIGHWAYS / VIA KYODO

Elsewhere, rising rivers in Hiratsuka, Kanagawa Prefecture, prompted the city government to order local residents to ensure their safety immediately.

Evacuation orders were also issued in the cities of Yokohama, Chiba and Shizuoka.

The heavy rain also affected transportation links. A section of the Tomei Expressway between Kanagawa and neighboring Shizuoka Prefecture and part of the Shin-Tomei Expressway in Shizuoka were closed to traffic. Bullet train operations were briefly suspended in sections between Tokyo and Shin-Osaka stations, according to Central Japan Railway Co.

The Meteorological Agency urged maximum caution and called on the public to be vigilant over mudslides, flooding and rising water levels in rivers.

Prefectural governments from Ibaraki in the east to Kyoto in the west have issued warnings to their residents about sediment-related disasters.

In the 72-hour period through 11 a.m. Saturday, 780 millimeters of rainfall was recorded in Hakone, Kanagawa Prefecture, and over 550 mm was logged in Gotemba, Shizuoka Prefecture, the agency said. Rainfall also reached 122 mm in the three hours to 2:40 a.m. Saturday in Kyoto.

All three figures marked the highest levels seen for July.

An area of Zushi, Kanagawa Prefecture, was hit by a landslide due to heavy rain. | KYODO
An area of Zushi, Kanagawa Prefecture, was hit by a landslide due to heavy rain. | KYODO

Atami saw rainfall of 313 mm in just 48 hours up to midnight on Saturday — above the monthly average of 242.5 mm in July, according to NHK.

The seasonal rain front is forecast to move toward the Sea of Japan coast over the weekend, with wide areas along the coast expected to see torrential rain through Monday.

In the 24 hours to 6 a.m. Sunday, rainfall was expected to total up to 150 mm in Tokai, up to 120 mm in the Kanto-Koshin region of eastern and central Japan, and up to 100 mm in the Kinki region and the northern part of Kyushu.

Rainfall in the 24 hours to 6 a.m. Monday is seen reaching up to 100-200 mm in northern Kyushu, up to 100-150 mm in Hokuriku and Tokai, and up to 50-100 mm in Kanto-Koshin and Kinki.

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