At least five people have been killed and five others reported missing after heavy rains pummelled the southern parts of South Korea, the state's disaster management agency has said.

The National Emergency Management Agency said four people were killed as torrential rains battered Busan, South Korea's second largest city.

The victims included two people who were trapped and drowned in their car as they drove through a submerged underpass in Busan.

An engineer was missing after he went down to a flooded building basement to check power lines in the city.

A flash flood into a swollen stream near the city of Changwon killed another person when a commuter bus was swept away.

Rescuers hammered their way through the windows and pulled out the body of a 19-year-old woman, still searching for the others missing, the AFP news agency said.

Four others aboard the bus were missing, including the driver. TV footage showed the bus being pulled downstream in muddy flood waters, and overturning before getting stuck beneath a bridge.

A nuclear power plant in nearby Gijang County was forced to halt operations as a cooling facility was inundated, while heavy rain knocked Busan's subway out of service for hours.

TV footage showed brown water cascading down stairways and escalators into the subway, and inundating railway tracks.

Southern Korea was hit by heavy rain in the space of just three hours on Monday.

Heavy rain warnings for Busan and the surrounding area were lifted later in the day.

Source: AFP