SEOUL: South Korea's military scrambled naval vessels to the western waters near the disputed maritime border with North Korea late Friday after an explosion ripped a hole in the bottom of a military ship, officials and news reports said.

The ship — reported to have 104 crew on board — began sinking off the coast of South Korean-controlled Baengnyeong Island close to North Korea around 10:45 p.m. (1345 GMT, 9:45 a.m. EDT), an official at the Joint Chiefs of Staff said, speaking on condition of anonymity in line with department policy.

He said the exact cause was not immediately clear. South Korea's Yonhap news agency reported an explosion in the rear of the 1,200-ton ship, but the official said he could not confirm the report.

Minutes later, Yonhap reported that another South Korean ship fired shots toward an unidentified target in the direction of North Korea. The Joint Chiefs official said he could not confirm the shooting but said the military was strengthening its vigilance in the area.

The incident comes amid heightened tension between the two Koreas, which remain in a state of war because their three-year conflict ended in a truce, not a peace treaty, in 1953.

President Lee Myung-bak convened an emergency meeting of security-related ministers, Yonhap said, citing presidential spokeswoman Kim Eun-hye.

Six naval ships and two coast guard vessels were rushed to the waters to rescue the crew of 104 on board the sinking ship, Yonhap said. More than 50 had been saved so far, the report said.