A South Korean naval vessel with 104 crew members onboard sank into waters off the west coast of the Korean Peninsula late Friday due to an unknown cause, local media reported, citing naval officials.

The 1,200-ton ship sank off the South Korean island of Baekryeongdo off the west coast around 21:45 p.m. Friday local time (12:45 GMT Friday), with an explosion in the back of the ship, and another South Korean naval vessel fired at an unspecified target toward the north in response, South Korea's Yonhap News Agency reported.

Lee Ki-shik, general of the South Korean Navy, confirmed in an press briefing that the ship "Cheonan" went down after the unexplained explosion ripped a hole in the ship's bottom.

The exact cause of the incident cannot be pinpointed at this moment, he said, adding that they also have been unable to determine whether it was caused by Democratic People's Republic of Korea (DPRK)'s navy vessel attack.

No casualties or injuries have been reported, but Lee said 58 out of the 104 crew members have been rescued thus far.

He said the military authorities will make efforts to find out the cause as soon as possible, and adopt corresponding measures.

Local media earlier reported that the incident might be caused by a possible torpedo attack from an unidentified DPRK vessel, citing military sources.

Local residents at Baekryeongdo reported having heard gunfire for about 10 minutes from 23:00 local time, local media added.

The South Korean government immediately convened an emergency meeting with security officials.

South Korea's Defense Ministry, while forming an emergency team to help rescue operations and find out the cause, cautioned against hastily linking the incident to a possible attack by the DPRK, according to Yonhap.

The incident occurred less than three months after tensions abruptly rose on the Korean peninsula following the DPRK's repeated firing of artillery shells earlier this year into waters near the de facto sea border, where the two Koreas had naval skirmishes before. Pyongyang refuses to acknowledge the maritime border, which was fixed unilaterally by the U.S.-led United Nations Command after the 1950- 1953 Korean War.