Bad weather, murky water and strong currents are hampering the search for survivors of the South Korean ferry disaster.
Emergency services are still searching for nearly 300 people missing after a ship carrying more than 470 people sank.
Officials say 179 people have been rescued. Most of the passengers were pupils at the same high school.
South Korea's president visited the wreck and urged rescuers to hurry.
Park Geun-hye said that time was running out and that every minute and every second was critical.
At least nine people are confirmed to have died, with dozens more injured.
Military divers have been fighting high wind and waves to try to access the vessel. Three divers were swept away in recent attempts but rescued by a fishing boat.
Naval and coastguard vessels used floodlights and flares, to maintain a search now involving more than 500 divers, 169 vessels and 29 aircraft.
But distraught relatives gathered in a gymnasium on nearby Jindo island insisted more should be done, and vented their grief and frustration to anyone who would listen.
"Get my child out of that ship! Dead or alive," one distraught father repeatedly shouted to rescue and local government officials."
The vessel was travelling from Incheon port, in the north-west, to the southern resort island of Jeju.
Some reports say the ferry went off its course and passengers' relatives are also questioning the role of the captain, who's being interviewed by police.
It is not yet clear what caused the ship to list at a severe angle and flip over, leaving only a small part of its hull visible above water, but some experts have suggested the ship may have hit an underwater obstacle.
The captain was being questioned, Yonhap news agency reported. "I am really sorry and deeply ashamed. I don't know what to say," Lee Joon-seok was shown saying on television.
Yonhap said the nine dead include four 17-year-old students and a 25-year-old teacher as well as a 22-year-old female crew member. Identities of the other three were not immediately known.
The latest figures say 475 people were on board, with 287 still unaccounted for. Figures issued by the government have changed several times, prompting criticism.
Efforts are concentrated on the ship, which sank in about 30m (100ft) of water.
"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.
Privately, some officials admit it is unlikely the remaining passengers will be found alive.
"Honestly, I think the chances of finding anyone alive are close to zero," a coastguard official told an AFP journalist on a rescue boat.
The US Navy has sent an amphibious assault ship, the USS Bonhomme Richard, to assist with the search.
Captain Joey Tynch told the BBC conditions were difficult.
"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," he said.
The ferry sent a distress call at around 09:00 local time (00:00 GMT) on Wednesday, about 20km (12 miles) off the island of Byungpoong. It sank within two hours, reports said.
At least 325 of the passengers on board the ship were students from Danwon high school in Ansan, near the capital, Seoul.
The students, aged 16 and 17, were heading on a field trip to Jeju island with about 15 teachers.
Survivors say they heard a loud thud, before the boat began to shake and tilt.
Some of the passengers managed to jump into the ocean, wearing life jackets, and swim to nearby rescue boats and commercial vessels.
But several survivors have said that they were told by crew members not to move.
"We must have waited 30 to 40 minutes after the crew told us to stay put," one unnamed rescued student was quoted as saying by AFP news agency.
"Then everything tilted over and everyone started screaming and scrambling to get out," he said.
Koo Bon-hee, 36, told the Associated Press that the rescue was not "done well". "If people had jumped into the water... they could have been rescued. But we were told not to go out."
Some of those trapped managed to send text messages to their relatives.
"Dad, don't worry. I'm wearing a life vest and am with other girls. We're inside the ship, still in the hallway," one girl told her father, AFP news agency reported.
But in a subsequent message she said she could not get out. "The ship is too tilted. The hallway is crowded with so many people."
Police, meanwhile, were investigating a text message reportedly sent to a relative of a missing student claiming some passengers had survived in an air pocket, Yonhap news agency said.
Police said they had not ruled out the possibility that the message was a prank, the agency said. There are no verified reports of communication from inside the sunken ship.
Kim Young-boong, an official from the company which owns the ferry, has apologised.
Japan's prime minister offered "heartfelt sympathy" to the victims and their families, and his government offered help with the search - a rare moment of detente between the feuding neighbours.
Shinzo Abe, whose strident nationalism has raised tensions between the two countries, said his thoughts were with those caught up in the tragedy.
The vessel - named Sewol - is reported to have a capacity of up to 900 people and is 146m (480ft) long.
Correspondents say this could turn out to be South Korea's biggest maritime disaster for more than 20 years.
Major maritime accidents in South Korea
1970: Sinking of passenger vessel Namyoung leaves 323 dead
1993: Sinking of passenger vessel Seohae Ferry leaves 292 dead
2007: Sinking of freighter Eastern Bright leaving 14 sailors missing
2009: Sinking of cargo ship Orchid Pia after a collision leaves 16 sailors missing
Thursday 17 April 2014
http://www.bbc.co.uk/news/world-asia-27056653
