SEOUL - A passenger ship carrying 462 people, mostly high students, capsized off South Korea's southwest coast Wednesday, leaving at least six dead and 284 others missing.

A 22-year-old female crew member and three high school students were the confirmed dead as of 9 p.m. local time (0000 GMT), with 174 people confirmed rescued, local media cited the country's central disaster and safety countermeasures headquarters.

Helicopters are seen above a South Korean passenger ship (C) that has been sinking, in the sea off Jindo April 16, 2014.[Photo/Agencies]

The death toll is expected to rise as hundreds of passengers were still missing around nine hours after the 6,825-ton passenger ship, "Sewol", sank off Jindo Island, near the southwest corner of the Korean Peninsula, at around 11:30 a.m. local time (0230 GMT) Wednesday.

Passengers rescued

S.Korea ferry sinks

The ship sent out a distress signal at 8:52 a.m. (2352 GMT Tuesday) and floated on its side for some two and a half hours before finally sinking.

Figures recorded by the headquarters showed the ferry carried 30 crew members and 432 passengers, including 325 high school students and 15 teachers, who were on a school excursion.

The ship departed South Korea's western port city of Incheon Tuesday night, heading for the southern resort island of Jeju.

Among those rescued were 78 high school students. Fifty-five people suffering minor injuries were transferred to nearby hospitals.

The Coast Guard suspended search operations inside the capsized hull at around 8 p.m. (1100 GMT) as faster-than-expected tidal currents and poor visibility thwarted divers. It will resume at around 1 a.m. (1600 GMT Wednesday) Thursday.

About 180 divers were sent to the scene during the night. Most of those missing were estimated to be trapped inside the sunken vessel, the Coast Guard said.

Other ships and helicopters were continuing to search waters near the scene. After receiving the distress signal, the South Korean authorities dispatched 72 rescue ships and scrambled 14 helicopters for rescue operations.

The U.S. Seventh Fleet said amphibious assault ship USS Bonhomme Richard, which has helicopters on board and was on a routine patrol off South Korea's west coast, was on its way to the scene to help.

But, salvage operations are unlikely to start before Friday morning as it will take time for three cranes to arrive at the scene.

The vessel was believed to have run aground as some rescued passengers said the ship began leaning to the port side after a thumping sound on the bow.

The ferry left its planned route as it departed two and a half hours late due to thick fog.

There was no Chinese passenger on board the vessel, according to the Chinese embassy in South Korea.

The cause of the sinking is still under investigation.

Korea Times reported the ship was not equipped with a voyage data recorder because it was a coastal ferry that sails relatively short distances.

Waters where the "Sewol" sank were known for strong tides, and there are many submerged rocks, it said. However, the Ministry of Oceans and Fisheries said the route the ferry was following had no such rocks, while Coast Guard officials said the route was often used by smaller ships.

A Korea Meteorological Administration (KMA) official said, "Visibility in the accident area seems not to have been so bad."

The KMA has an observatory on nearby Jindo Island, but could not check the site's exact weather conditions. "Localized fog banks can occur in small areas," the KMA official said.

The ship's operator, Chonghaejin Marine, had apologized for the accident and vowed to focus on rescue efforts.

A company official was quoted by the Korea Herald as saying that the vessel did not deviate significantly from course, and the company was preparing to recover the ferry.

The captain of the Sewol is a veteran with eight years of experience on the Incheon-Jeju Island route. The 69-year-old man, surnamed Lee, joined Chonghaejin Marine in November 2006. He was the most experienced of the three captains operating the company's large ferries, a Chonghaejin employee said.

Lee was filling in for the Sewol's usual captain, who had gone on vacation.

A Chonghaejin Marine official said there should be no problem with 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 out of Incheon and 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 from Incheon to Baengnyeongdo Island in the West Sea. The 396-ton ferry was carrying about 140 passengers and no injuries were reported.

South Korean President Park Geun-hye was immediately briefed on the accident, and she ordered maximum efforts be made to rescue all passengers, stressing that all available Navy, Coast Guard and other nearby vessels should be mobilized.

"There is not much time left before sunset. Please make the best efforts to rescue even one more person," she said during a visit to the central disaster management office in Seoul. Park said she felt "truly devastated."

Cargo ship sinks off ROK, 9 die