At least 10 people were missing after the deluge, and rainfall was expected to intensify in the next few days.
Powerful monsoon rains swept across South Korea, burying homes, knocking down trees, canceling flights and trains, and cutting power to tens of thousands of residents, officials said on Saturday.
The downpour caused flooding and landslides in the country’s central region, leaving at least 26 people dead and 10 others missing as of late Saturday local time, the Interior Ministry said, adding that the rainfall was expected to intensify in the coming days.
Heavy monsoon rains are typical in South Korea in the summer, and its mountainous topography makes it susceptible to landslides. But the number of casualties reported on Saturday was unusual.
“The death toll is surprisingly high,” Cheong Tae Sung, an expert in flooding with South Korea’s National Disaster Management Research Institute, said in an interview, adding that there were a couple of possible reasons for this.
One is that in recent years rainfall has tended to be concentrated in urban areas, near the large cities of Busan and Seoul. This time, much of the recent rains fell in rural parts of Chungcheong and Jeolla Provinces, which can be more vulnerable in part because they are more difficult to monitor and reach.
Mr. Cheong added that, as climate change warms South Korea, rain also appears to be coming in more intense bursts rather than slowly over a longer period. That shift has made preparing for floods harder.
At least five of the people killed on Friday and Saturday died inside homes and buildings that had collapsed in landslides, and one person was buried in earth and sand, the Interior Ministry said in a statement. Another victim died after a road collapsed underneath.
Several dams in the central part of the country began the controlled release of water on Saturday, and one overflowed, prompting the evacuation of thousands of residents living downstream. A passenger train derailed on Friday night when soil entered a railroad track, though no casualties were reported.
More than 5,500 residents have evacuated their homes since Thursday, according to the ministry statement, which urged emergency workers to help evacuate residents and conduct rescues.
The Korea Meteorological Administration said on Saturday that the rain would get stronger over the next two days, mainly in the central and southwestern parts of the country.
The South Korean government has been on alert this month, with top officials stressing the importance of safety during the monsoon season. That sense of urgency grew stronger over the weekend, as reports of deaths and injuries began to come in.
“If there is even a small possibility of danger, overreaction is the principle of this heavy-rain response,” Prime Minister Han Duck-soo said on Saturday, mobilizing the military to join rescue efforts. President Yoon Suk Yeol repeated his calls for an “all-out response” by the government.
Parts of central South Korea were under a heavy rain advisory on Saturday morning, with up to 1.6 inches expected in a single hour in some places later in the day, the ministry said. Some regions should expect up to nearly 10 inches of precipitation to accumulate, it added.
South Korea’s monsoon season typically begins in June and ends in early August. The rest of the year is mostly dry and sunny, and spring brings the risk of wildfires.
The country used to experience heavy casualties and in 1984 accepted humanitarian aid from North Korea. More recently, annual flood-related deaths have been in the single digits, except in 2011, 2020 and 2022.
In August, some of the heaviest rains in decades led to the deaths of at least 14 people nationwide. In 2020, weeks of intermittent rain caused flooding and landslides across the country, killing 48 people. In 2011, more than 70 people died, including 17 who were killed when mudslides crashed into residential buildings in southern Seoul.
Mike Ives contributed reporting.