A South Korean vessel fired at an unidentified vessel towards the north and the South’s presidential Blue House was holding an emergency security meeting, Yonhap news agency said.

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

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.