At least 17 people have been killed after two separate landslides hit South Korea, officials say.

They said rescue workers on Wednesday were helping those trapped and searching for missing people in the affected areas.

The first landslide crashed into a mountain resort in Chuncheon, killing five people and leaving two people missing, the officials said.

Eight of those killed in the early morning disaster were college students who had been doing volunteer work.

They were staying in a resort cabin in Chuncheon, about two hours northeast of Seoul, when the mud and debris engulfed them, Byun In-soo of the town's fire station said.

About 500 rescuers searched for two students who were still missing after the landslide.

Separately, in southern Seoul, five people were killed in Wednesday's second landslide, a police official in the Bangbae area said.

The dead had not yet been identified. One child was also missing.

Fast-moving muddy water filled the streets. Local broadcaster YTV showed the dramatic rescue of group of people who had scrambled onto the roofs of their partially submerged cars to escape the gushing water.

Elsewhere, water filled some subway stations and spewed from sewers.

About 800 houses flooded, according to a city disaster official who declined to be named because of office policy.

South Korea has been buffeted by strong rain this week: about 400mm of rain fell in Seoul in just 17 hours starting on Tuesday afternoon.

More than 250mm fell on Chuncheon in the last two days.

Weather officials say another 10 inches could fall till Friday in the north of the country.