A blast of heavy rain sent landslides barrelling through South Korea's capital and a northern town Wednesday, killing at least 32 people, including 10 college students doing volunteer work.

The students died as mud and debris engulfed them as they slept in a resort cabin in Chuncheon, about 110 kilometres northeast of the capital Seoul, said Byun In-soo of the town's fire station. A married couple and a convenience store owner also died.

About 500 officials and residents worked to rescue people trapped in the mud and wreckage. Twenty-four people were injured and several buildings destroyed, officials said. Witnesses interviewed on television likened the sound of the landslide to a massive explosion or a screaming freight train and described the screaming they heard as buildings were carried away by rivers of mud.

In southern Seoul, 16 people died when mud crashed through residences at the foot of a mountain, emergency official Kim Jong-seon said. Three others also died after a stream just south of Seoul flooded, Kim said, and 10 people were reported missing throughout the country.

The heavy rain also left about 620 people homeless and flooded 720 houses and about 100 vehicles throughout South Korea, the National Emergency Management Agency said in a statement.

South Korea has been pummeled with strong rain this week. About 400 millimetres fell in Seoul in just 17 hours starting Tuesday afternoon. More than 250 mm fell on Chuncheon in the last two days. Weather officials said more rain could fall in northern South Korea, including Seoul, through Friday.

Water fills subways

Fast-moving muddy water filled streets in Seoul on Wednesday, with people scrambling to the roofs of their partially submerged cars. Water filled some subway stations and spewed from sewers. TV images showed people in one flooded subway station using shovels, brooms and a wooden board in an effort to keep more rain from coming in.

Local TV showed officials rescuing hikers stranded on mountainsides. People plodded down streets covered with knee-deep water, many barefoot, their pants rolled up. Cars were restricted from entering the lower part of a two-level bridge in the centre of Seoul because it was submerged.

The Seoul Metropolitan Police Agency issued a traffic emergency, mobilizing more officers to deal with the problems caused by the heavy rain.

Seoul shut down portions of two major city highways stretching along each side of the main Han River because of high water levels, Kim Ji-hwan, a disaster control official, said.

A dam located just east of Seoul was discharging 14,900 tonnes of water per second, Cha Jun-ho, an official at the government's Han River Flood Control Office, said. The dam discharged about 900 tonnes per second days before the recent downpours began.

Fire officials also worked to reach about 60 houses that were cut off from roads in Seoul's Hyeongchon village because of the heavy rain, a local officer said, declining to be identified because of office procedure.

People in Seoul, where smartphones are ubiquitous, posted dozens of photos on Twitter and Facebook showing inundated streets and mud-covered cars. Many complained online that Seoul had neglected to prepare for the downpours.