A South Korean naval ship was sinking on Friday after possibly being hit by a North Korean torpedo and several sailors were killed, South Korean media reported.

A South Korean warship later fired at an unidentified vessel toward the north, indicating a possible attack, and the South's presidential Blue House was holding an emergency security meeting, the Yonhap news agency said.

"The ship appears to have begun sinking after an explosion at the rear of the ship," Yonhap quoted the South Korean Navy saying in a statement. "We have been unable to find the exact cause of the incident as of this moment."

The incident comes as destitute North Korea is facing pressure to end its year-long boycott of international nuclear disarmament talks, where it can win aid to prop up its broken economy in exchange for reducing the security threat it poses.

... South Korea's YTN TV network said the government was investigating whether the sinking was due to a torpedo attack.

But the network also quoted a government source saying it was unclear yet whether the incident was related to North Korea.

"We are currently focusing on rescuing people," the source said.

The incident took place near a disputed Yellow Sea maritime border off the west coast of the peninsula that was the scene of two deadly naval fights between the rival Koreas in the past decade.

Yonhap said the 1,500-ton ship with 104 crew aboard began sinking around 9:45 p.m. (0845 EDT)

Local media reports said at least 59 South Korean sailors survived the attack and an unknown number appeared to have been killed or were missing. A rescue operation was under way.