SEOUL, South Korea April 16, 2014 -- Divers and ships searched the cold waters off South Korea's coast for hundreds of missing people today after a ferry loaded with high school students suddenly shifted and sank.

The ferry, identified as the Sewol, was carrying 475 people to the southern island of Jeju when it sent a distress call as it began leaning to one side.

Survivors said the ferry was shaking, but they were told by the crew to stay put. The ship then suddenly titled sharply and the passengers said they were hit by shifting bags, refrigerators and other debris.

Passenger Kim Seong-mok, speaking from a nearby island after his rescue, told YTN that he was "certain" that many people were trapped inside the ship as water quickly filled with water and the severe tilt of the ferry kept them from reaching the exits. Some people yelled at those who couldn't get out, urging them to break windows.

Kim said that after having breakfast he felt the ferry tilt and then heard it crash into something. He said the ferry operator made an announcement asking that passengers wait and not move from their places. Kim said he didn't hear any announcement telling passengers to escape.

Photos: Sadness, Desperation as Ferry Sinks Off South Korea's Coast

Nine are confirmed dead and 287 are missing. The number of rescued was put at 179.

More than 300 of the passengers were students from Danwon High School in Ansan, near Seoul, who were on a school trip.

Dozens of boats, helicopters and divers scrambled to rescue passengers. Video shows rescue crews boarding the ship as it floated on its side helping people off, and helicopters throwing rafts into the water speckled with bobbing heads.

The ship slowly turned upside down and later sank more than 100 feet below the water's surface.

Divers searching for survivors were hampered by the muddy bottom with limited visibility to about 15 inches.

The water temperature was also a danger to potential survivors. At 55 degrees Farenheit it could cause hypothermia after about 90 minutes or 2 hours, according to an emergency official who spoke on condition of anonymity citing department rules.

The students were on their way to Jeju island for a four-day trip. The trip from Incheon to Jeju is usually about 14 hours, so the ferry was about three hours from its destination when it made the distress call.

At the high school, students were sent home and parents gathered for news about the ferry.

The ship sank near the tiny Jindo Island and survivors are gathered there at the only gym on the island.

Officials said two large cranes are en route to the sunken ship in an effort to raise it, but the cranes won't arrive for another day.

The Associated Press contributed to this report.