Police said the crew consists of six South Koreans and six Vietnamese.

President Moon Jae-in instructed related authorities to mobilize every possible means for the search-and-rescue efforts, according to Cheong Wa Dae spokesperson Ko Min-jung.

He stressed the importance of swift operations amid reports that waves are high and the water is cold around the accident site.

Moon instructed the interior and safety minister and the maritime minister to thoroughly manage the situation to ensure effective joint operations by the Coast Guard, the Navy and local authorities.

The president also ordered the authorities to inform the families of victims, including the Vietnamese crew, of progress in rescue work as early as possible, Ko added.

A Navy vessel, helicopters, ships and civilian boats have been mobilized to rescue the missing crew members.

However, strong winds and high waves are blocking some of the smaller rescue boats from approaching the accident scene, according to maritime police.

"The fire was big enough that it was difficult to enter the ship even after the (Navy) vessel arrived," an official said.

"Since there is a possibility of finding crew members on the ship, we plan to search the inside of the ship once weather conditions improve." (Yonhap)