Torrential rains have caused flooding, landslides, and power cuts across much of the country.

At least 26 other people are known to have been killed, while ten remain missing.

It is unclear how many people are still trapped in the tunnel - which is 685 metres long - but 15 vehicles are thought to be submerged.

Officials said the tunnel in Osong - near the city of Cheongju in the central North Chungcheong province - was swamped by a flash flood, which happened too quickly for drivers and passengers to escape after a nearby river burst its banks.

On Sunday morning, six bodies were recovered from inside a bus. That followed the discovery of one other body and the rescue of nine survivors on Saturday.

Local media reported that the latest deaths brought the overall toll from the floods to at least 33.

Most of the other fatalities have been in the mountainous North Gyeongsang region, where landslides have swept away whole houses.