Parts of South Korea were battered by torrential rains on Thursday, with one region pummelled by the most rainfall per hour since full records began in 1904, the country's weather agency said.

South Korea typically experiences monsoon rains in July but three areas in the country's South Chungcheong province experienced some of the heaviest hourly downpours on record this week, official weather data showed.

The western Seosan area was hit by rainfall peaking at 114.9 millimetres per hour, "a level typically seen only once in 100 years", a weather agency official said, adding that this was the highest rate since 1904.

The heavy rains were due to "warm and moist air flowing in along the edge of the North Pacific High, triggering strong atmospheric instability", the official added.

South Korean broadcasters ran videos of severe flooding in Seosan, with water swamping markets and apartment complexes, as well as submerging parked cars.

Residents in Hongseong county, also in South Chungcheong province, were ordered to "evacuate immediately to a safe location" early on Thursday due to flooding from a nearby stream.

Several schools and nurseries in the county were also closed.

One driver was killed in Osan, a city about 50 kilometres south of Seoul, after a 10-metre-high retaining wall from an overpass collapsed onto the road, crushing his car.

In Chungcheong province, two people were rescued following a landslide. (AFP)