Six South Koreans went missing around Sunday 6 a.m. near the Imjin River in Yeoncheon, Gyeonggi Province, due to flooding apparently caused by discharge of a North Korean dam.

Rescue operations have continued into early Monday morning, with two-thousand rescue workers --- double that of Sunday --- mobilized for the search.

On Sunday, several hundred soldiers and police forces searched the area using six helicopters, 15 rafts and four large vessels.

Search efforts have yet to bear fruit due to rough waves, an extensive search area and many areas with limited access.

According to the Unification Ministry, North Korea says water is "naturally discharged when the water level reaches the maximum height."