Emergency rescue teams are searching for 287 of the 425 reported to be aboard the MV Sewol. Officials said 179 people have been rescued, most of them high school students, and the search was on for the others. Around 325 of the 425 passengers aboard were students from Danwon high school in Ansan, near Seoul, on a field trip to Jeju island with 15 teachers.
South Korean President Park Geun-hye said that time was running out for the survivors and urged rescuers to hurry as every second was critical.
Military divers had to brave high winds and waves to gain access to the vessel but were unable to get into any of the cabins, according to the chief of the West Regional Headquarters of the South Korean Coast Guard, Kim Soo-hyun.
The whipping currents have also mades the waters murky reducing visibility to almost zero.
"We carried out underwater searches five times from midnight until early in the morning, but strong currents and the murky water pose tremendous obstacles," said Kang Byung-kyu, minister for security and public administration.
The U.S. Navy has sent an amphibious assault ship, the USS Bonhomme Richard, to assist with the search.
"We found ourselves in challenging weather conditions today -- very low cloud ceilings and reduced visibility and rain, and we're working a search area around the site in close co-ordination with the South Korean on-scene commander," said Captain Joey Tynch, who spoke to the BBC.
Overnight, naval and coastguard vessels used floodlights and flares to continue the search, involving 500 divers, 171 vessels and 29 aircraft, despite the precarious conditions. Cranes are expected to reach the site Saturday.
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