SEOUL, July 15 (AFP) - Seven people have been killed and three were missing as heavy rains flooded South Korea, officials said Saturday, with thousands told to evacuate their homes due to an overflowing dam.

Over the last three days, heavy rainfall has submerged counties across the country, with local media reports suggesting the death toll may rise later Saturday.

More than 6,400 residents in the central county of Goesan were ordered to evacuate early Saturday as the Goesan Dam began overflowing from the downpour and submerging low-lying villages nearby, the interior ministry said.

The seven people killed since Friday died in rain-related landslides and building collapse, it added.

Two of the three people reported missing were swept away when a river overflowed in North Gyeongsang province, the ministry said.

All regular train service nationwide was suspended as of 2:00 pm (0500 GMT), although KTX bullet trains remained operational with potential schedule adjustments, according to the Korea Railroad Corporation.

South Korean Prime Minister Han Duck-soo urged officials to respond to river overflows and landslides "preemptively", and requested support for rescue operations from the defence ministry.