At least 31 people have died in South Korea as a result of heavy rain and thousands across the country have been forced to evacuate their homes, Yonhap reported on Sunday. 

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

In the most severely affected areas, "entire houses were swept away whole," one emergency responder told Yonhap.

According to the central disaster and safety countermeasure headquarters, a total of 4,763 households were evacuated due to the damage from the downpours.

More than 6,400 residents in the central county of Goesan were ordered to evacuate early Saturday as the Goesan Dam began overflowing and submerging low-lying villages nearby, the Interior Ministry said.

Some of the people who have been reported missing were swept away when a river overflowed in North Gyeongsang province, the ministry said.

According to Yonhap, rescue workers were battling to reach some 19 cars trapped in an underground tunnel in Cheongju, North Chungcheong province, where one person was found dead.

Flash flooding swept through the area too quickly for people to escape, but water levels remain high, and it is unclear how many people were trapped inside their vehicles, Yonhap reported.

The number of deaths is expected to rise as local government agencies assess the damage nationwide, the news agency said.

All regular train services nationwide were suspended as of 2 p.m. local time, although KTX high-speed trains remained operational with potential schedule adjustments, according to the Korea Railroad Corporation.

Roads were closed, and trails in national parks shut due to the rain and flooding.

The Korea Meteorological Administration issued heavy rain warnings, saying more rain was forecasted through to Wednesday next week, and the weather conditions pose a "grave" danger.

South Korean President Yoon Suk-yeol has held a meeting with his aides on the government's response to heavy rain and flooding in South Korea, Yonhap  reported on Sunday, citing Yoon's office.

Yoon is also scheduled to be briefed on the damage from the rain in a video conference with Prime Minister Han Duck-soo and relevant ministers.

(With input from agencies)