The death toll from flooding and landslides caused by heavy rains in South Korea climbed to 37 on Sunday.

South Korea is at the peak of its summer monsoon season, and there has been heavy rainfall for the last four days, causing a major dam to overflow.

The Interior Ministry reported that 37 people were killed and another nine were missing nationwide in the heavy downpours, mostly buried by landslides or after falling into a flooded reservoir.

Hundreds of rescue workers were still struggling to reach more than 10 cars and an unknown number of people trapped in a 430-meter (1,410-foot) underground tunnel in Cheongju, North Chungcheong province, the ministry said.

When AFP arrived at the site Sunday, rescue workers were trying to drain the tunnel to reach victims but the water still appeared to be too deep, hampering search efforts.

The tunnel was inundated Saturday morning after floodwaters swept in too quickly for the vehicles inside to escape, according to the Yonhap news agency.

Five people were rescued from a bus in the tunnel Saturday, and nine bodies have so far been pulled from the site, with divers working around the clock searching for more victims, the ministry said.

The police have received missing person reports for 11 people believed to be in the tunnel, but a final official toll has not yet been provided, as it is unclear how many people were in each car, Yonhap reported.

"I have no hope but I can't leave," a parent of one of those missing in the tunnel told Yonhap.

"My heart wrenches thinking how painful it must have been for my son in the cold water."

Images broadcast on local television showed a torrential stream of water from a nearby river that had burst its banks flooding into the tunnel, as rescue workers struggled to use boats to get to people inside.

More rain

South Korean President Yoon Suk Yeol, who is currently on an overseas trip, held an emergency meeting with his aides on the government's response, his office said.

Earlier, he ordered Prime Minister Han Duck-soo to mobilize all available resources to minimize casualties.

The majority of the casualties – including 19 of the dead and eight of the missing – were from North Gyeongsang province and were largely due to massive landslides in the mountainous area that engulfed houses with people inside.

Some of the people who have been reported missing were swept away when a river overflowed in the province, the interior ministry said, and more than 1,500 people have been unable to return after evacuating from their homes.

The Korea Meteorological Administration forecast more heavy rain through Wednesday, and urged the public to "refrain from going outside."

South Korea is regularly hit by flooding during the summer monsoon period, but the country is typically well-prepared and the death toll is usually relatively low.

Scientists say climate change has made weather events around the world more extreme and more frequent.

South Korea endured record-breaking rains and flooding last year, which left more than 11 people dead.

They included three people who died trapped in a Seoul basement apartment of the kind that became internationally known because of the Oscar-winning Korean film "Parasite."

The government said at the time that the 2022 flooding was the heaviest rainfall since Seoul weather records began 115 years ago, blaming climate change for the extreme weather.