Media playback is unsupported on your device Media caption Lucy Williamson: Images reveal how quickly the ship went down

Almost 300 people remain unaccounted for after a ferry carrying 459 people capsized and sank off South Korea.

The ferry, carrying mainly school students, was travelling from the port of Incheon, in the north-west, to the southern resort island of Jeju.

Analysis South Korean TV networks are constantly replaying dramatic footage of the rescue efforts before the ferry sinks. It shows an armada of small boats motoring right up beside the ferry, which listed heavily on its side before sinking. Rescuers are seen desperately grabbing teenagers out of the water before they are swept away by the currents and undertow. Other footage shows helicopters throwing orange life rafts to passengers bobbing on the sea. Some of the passengers are then winched to safety. What makes this accident even more distressing is the fact that among those on board were high school students on a trip to a holiday island. Relatives and friends of those on board are posting on social media sites asking for any news or information about loved ones. On Facebook many South Koreans are re-posting a yellow ribbon to symbolise the hope that the missing may still be found alive. "Please, please survive and come back," the message reads. "We love you guys." Dramatic rescue

Emergency teams are using floodlights and flares to search the stricken vessel through the night. Those rescued have been taken to a nearby island.

Four people are now said to have died and dozens of others have been hurt.

South Korean officials had earlier said that 368 people had been plucked to safety, but later said there had been a counting error.

They have now revised down the number rescued to 174.

Images showed the ferry listing at a severe angle and then later almost completely submerged, with only a small part of its hull visible. It sank within two hours of sending a distress signal, reports said.

There are fears this could turn out to be South Korea's biggest maritime disaster for more than 20 years, says the BBC's Martin Patience in Seoul.

Cause unclear

Several coast guard, military and commercial vessels were involved in the rescue effort, which unfolded rapidly on Wednesday morning.

Pictures from the scene showed rescue teams balanced on the sinking hull pulling teenagers from cabin windows. Some of their classmates jumped into the sea as the ship went down.

Reports suggest some of those rescued were picked up by nearby commercial vessels.

The US Navy has sent an amphibious assault ship, the USS Bonhomme Richard, to assist with the search, officials say.

MV Sewol Passengers on board: 459

Maximum capacity: 900

Length: 146 metres

Built: 1994





REUTERS

Image copyright AP Image caption Military and civilian ships and helicopters have been searching for survivors

Image copyright AFP Image caption Reports said the ship capsized and sank within a period of two hours

Teams of navy divers were now searching the scene for those unaccounted for, officials said, but the work was challenging.

"There is so much mud in the sea water and the visibility is very low," said Lee Gyeong-og, vice-minister of security and public administration.

One body, of a female crew member, had been recovered from the ship, the coastguard said. Another person, a male high school student, died after being rescued.

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 Source: Yonhap

One student told local media her friends became trapped.

"Currently, I am in the middle of being rescued. At the time, the ship was turning on its side, and none of us were moving as we were told not to move as it was dangerous," the unnamed student said.

"So, I am not well aware of the situation, but I am told that my friends and other friends could not escape as the passage was blocked. It seems that there are many students who could not get out as the passage was blocked by water."

It is not yet clear what caused the incident, but witnesses described hearing an impact, before the ship listed and quickly sank.

One passenger told the YTN news channel: "We heard a big thumping sound and the boat stopped."

Image copyright AFP Image caption Teams have brought rescued passengers to shore - at least 13 are reported to be hurt

Image copyright Reuters Image caption Flares light up the sky as the search for missing passengers continues through the night

Image copyright AP Image caption Relatives of the missing are waiting to hear of the fate of their loved ones

"The boat is tilting and we have to hold on to something to stay seated," the passenger said.

Another passenger said the ship was "shaking and tilting", with people tripping and bumping into each other.

Media playback is unsupported on your device Media caption Survivor: "There was an announcement telling us to sit still, but the ferry was already sinking"

South Korean President Park Geun-hye has expressed sadness over the incident, saying it was "truly tragic" that students on a field trip were involved in "such an unfortunate accident".

Kim Young-boong, an official from the company which owns the ferry, has apologised.

Analysis Domestic ferries across some parts of Asia have a bad safety record, especially in countries such as the Philippines and Indonesia where ships can be overcrowded and poorly maintained. But in recent years South Korea has been one of the exceptions. This particular ferry was built in Japan, who make some of the best ships in the world. It wasn't anywhere near full and it was travelling a well-worn route in reasonably calm seas. The speed with which it flipped over and sank is a major concern. Passengers described a loud thud, which might suggest it hit something hard. It doesn't matter how well built the ship is, collisions can sink vessels very quickly. Survivors have also complained that they were told to stay put even though the ferry was tipping over. That's not as surprising as you might think. The basic assumption is always that the ship is the best lifeboat. That it's normally safer to stay on board than brave the water. All of these split second evacuation decisions and the design of the ship, will be analysed by investigators.

"I would like to say sorry to the passengers, which include a number of students and their parents, and promise that our company will do its best to minimise loss of life. We are sorry," he said, according to the AP news agency.

South Korea ferry Ferry - named Sewol - was travelling from Incheon to Jeju Island, a route it serves twice a week

The 146m-long vessel has a capacity of about 900 people but was carrying about 470 people

Passengers include about 330 students from Danwon High School in Ansan, a suburb of Seoul

Weather conditions were described as fine. Yonhap news agency said that the ferry sank at a depth of 30m (90ft).

News agencies said the ferry had sent out a distress signal about 20km (12 miles) off the island of Byungpoong at about 09:00 local time (00:00 GMT).

"We will try to determine the cause of the accident after rescue operations are over," said Lee Gyeong-og.

Many of the passengers were students from a high school in a suburb of Seoul heading off on a four-day field trip to Jeju.

Angry parents have gathered at the school in Ansan to demand answers, reports the BBC's Lucy Williamson in Seoul.

Earlier reports put the number of passengers on the ferry at about 350. The vessel is reported to have a capacity of up to 900 people.

Lee Gyeong-og, the vice-minister of security and public administration, was quoted by the AP news agency as saying that 30 crew members, 325 high school students, 15 school teachers and 89 non-student passengers were aboard the ship.