Six South Koreans camping and fishing along a river flowing from North Korea were missing Sunday after it suddenly rose, possibly because a new dam in the North released a large amount of water without warning, The Associated Press reported Sunday, quoting officials.

About 200 rescuers were trying to locate the missing people along the Imjin River, fire official Park Ju-il was quoted as saying. He said their identities were not immediately available.

Gyeonggi provincial official Choi Kwon-rak said a North Korean dam just north of the border may have released large amounts of water without notice, according to AP.

Choi said there was no proof that the North had done so, but there was no other apparent reason for the river to rise so abruptly because it had not rained in the area for several days.

He said the river's water level had been about 7.5 feet (2.3 meters) before it suddenly jumped to 15.1 feet (4.6 meters) Sunday morning.

South Korean officials believe North Korea plans to use water from the Hwanggang Dam for power generation and crop irrigation. Some officials have raised concerns that the dam could cause water shortages or flooding in the South, and could be used by the North as a weapon.

Construction of the dam was about 95 percent complete early last year, and it was believed to have a capacity of 400 million tons of water, according to earlier South Korean government estimates.