SEOUL - A massive operation is underway off the coast of Jindo Island where a ferry carrying more than 450 passengers and crew sank on Wednesday, killing at least four people and leaving almost 300 still unaccounted for.
As of Wednesday night, 174 people were rescued and 284 still unaccounted for, Korea Herald reported.
It said the four dead included a woman identified as 22-year-old Park Ji Young, a staff worker for the ferry company Chonghaejin Marine, and Jung Cha Woong, a student at Danwon High School.
In Singapore, the Ministry of Foreign Affairs said it has not received any report of Singaporeans on board the South Korea ferry.
"We have not received reports that there were Singaporeans on board the South Korean ferry which sank on April 16," a ministry spokesman told The Straits Times.
Korea Herald said the rescue operation involved elite navy divers as well as vessels and helicopters from the navy, coast guard, air force and the army. Underwater search is expected to be in full swing early Thursday.
In addition, US Navy ship Bonhomme Richard joined the rescue efforts and the US 7th Fleet also said that it would provide support as necessary.
The 6,325-ton Sewol began to sink at about 8.55 am local time on Wednesday off the coast of Jindo on its way to Jeju Island from Incheon. According to the Ministry of Oceans and Fisheries, however, the Sewol began to drift in an unexpected direction from 8.52 am.
Passengers on board the ferry included 324 students and 14 faculty members from Danwon High School who were travelling to Jeju Island on a school trip.
The government had launched a central response centre, with President Park Geun Hye ordering authorities to concentrate on rescue efforts.
"Efforts should be made to prevent even one casualty, and a thorough search (of the ship) must be carried out to ensure nobody is left behind," Ms Park was quoted as saying by Mr Lee Gyeong Og, second vice minister of security and public administration.
The president also visited the central response centre and urged the officials to pick up the pace of the rescue operations as sunset was approaching.
Rescue workers arrived at the scene at 9.30am, about half an hour after the emergency call from the Sewol, but the search for survivors was hampered by strong currents.
Korea Herald reported that the passengers were initially told to stay put, but began jumping into the sea following an onboard announcement that the ship was about to sink completely as rescue efforts were underway.
With survivors saying that power inside the ship was cut off as it was sinking, it is speculated that many may have been trapped inside.
"A search was conducted within a 5-kilometer radius, but no recoveries were made. Considering the water temperature, depth and the time lapsed, anyone trapped inside is unlikely to have survived," a rescue worker told a local news network.
The depth of the sea where the ship sank is reported to be over 45 metres, with a reported water temperature of about 12 deg C.
Korea Herald said the cause of the accident was not yet determined but the passengers suggested that the ferry hit a reef just before 9am when the vessel jolted with a loud noise.
Rescued passengers also speculated that thick fog may have contributed to the accident, but the meteorological office said the area was clear with visibility of about 20 kilometres.
It is also speculated that the ferry may have altered course in order to make up for time lost due to its departure being delayed by weather conditions.
Chonghaejin Marine apologised for the accident and vowed to focus on rescue efforts.
A company official said the vessel did not deviate significantly from course, and that the company was making preparations to recover the ferry.
The captain of the Sewol is a veteran with eight years of experience operating the Incheon-Jejudo Island route. The 69-year-old man surnamed Lee joined Chonghaejin Marine in November 2006. He is the most experienced of the three captains operating the company's large ferries, according to a Chonghaejin employee.
He had been operating a different 6,325-ton ship before he was switched to the Sewol in March 2013. He was sent on the day of the accident to operate the Sewol to fill in for the main captain, who had gone on vacation.
"Lee is a substitute captain, who fills in for the Incheon-Jejudo Island route when the two captains assigned to the route go on vacation," a Chonghaejin Marine official said. He added that there should be no problem with Mr Lee operating the ship, as qualification for a substitute captain requires approval by the Incheon Regional Maritime Affairs and Port Administration.
The company operates four vessels including the Sewol on three routes, which set out from either Incheon or Yeosu, as well as river taxis on the Hangang River.
This is the second accident involving a Chonghaejin Marine vessel in three weeks.
On March 28, another Chonghaejin ferry hit a 7.93-ton fishing boat en route to Baengnyeongdo Island in the West Sea from Incheon. The 396-ton ferry was carrying about 140 passengers and no injuries were reported.
No irregularities were found on the Sewol during a safety check conducted in February.