Vehicles swept away by sudden rising water are partially submerged in the Imjin river near the demilitarized zone separating the two Koreas in Yeoncheon, about 62 km (39 miles) north of Seoul, September 6, 2009. [Agencies]

SEOUL: The Republic of Korea (ROK) on Monday lodged a complaint to the Democratic People's Republic of Korea (DPRK) over an unannounced discharge of water from a dam, which may be the cause of the disappearance of six people, the ROK's Unification Ministry said.

It also asked for pre-notification in the future to avoid a similar tragedy, Chun said.

The message was sent through an inter-Korean hotline in the name of the Minister of Land, Transport and Maritime Affairs Chung Jong-hwan, who is in charge of flood-related issues.

Six ROK campers, including one child, went missing Sunday morning while camping at a riverside sites in Yeoncheon, downstream of the Imjin River, which originates in the DPRK, local police and rescue said.

The missing were apparently swept away by a huge wave released by a dam in the DPRK, police said, adding that the discharge of water caused the river's water levels to surge from 2.3 meters to 4.96 meters suddenly.

Almost no rain has fallen in the area in recent days, police said, adding that they were investigating the cause of the accident.