MOKPO, South Korea - Fears rose Thursday for the fate of 289 passengers still missing more than 24 hours after their ferry flipped onto its side and filled with water off the southern coast of South Korea.

A coast guard official said the death toll was confirmed at seven, but that is expected to rise sharply because the missing have spent more than a day either trapped in the ferry or in the cold seawater. Coast guard officials put the number of survivors early Thursday at 179.

There were 475 people aboard - many of them high school students on a class trip - and frantic parents have gathered at their school near Seoul and in Mokpo in the south of the country, not far from where the ferry slipped beneath the surface.

Divers, helicopters, and boats continued their search Thursday for survivors.

Some early reports had said all students and teachers from the school - 340 people in all - had been rescued, but officials later said those accounts were wrong.

It was still not known why the ferry sank, but coast guard officials were interviewing the captain and crew amid reports the ferry may have deviated from a government-advised route, perhaps because of high winds and fog. The ferry broke away from the route advised by the Ministry of Oceans and Fisheries, Yonhap News reported, citing the coast guard.

Strong currents and low visibility were making operations difficult Thursday as more than 500 divers try to search the vessel, Kang Byung Kyu, minister of Security and Public Administration, said at a televised briefing Thursday.

Rescuers hoped some passengers may still be alive if there are enough air pockets in the ship. Media reports said submersibles were pumping oxygen into the hull, although the coast guard declined to comment.

The Sewol, a 480-foot vessel that can hold more than 900 people, set sail Tuesday from Incheon, in northwestern South Korea, on an overnight, 14-hour journey to the tourist island of Jeju.

The ferry was three hours from its destination when it sent a distress call after it began listing, the Ministry of Security and Public Administration said.

Passenger Kim Seong Mok told broadcaster YTN that after having breakfast, he felt the ferry tilt and then heard it crash into something. He said he was certain many people were trapped inside the ferry as water rushed in and the severe tilt of the vessel kept them from reaching the exits.

Koo said many people were trapped inside by windows that were too hard to break.

"The rescue wasn't done well. We were wearing life jackets. We had time," Koo, who was on a business trip to Jeju with a coworker, said from a hospital bed in Mokpo, the nearest major city to the site of the accident, where he was treated for minor injuries. "If people had jumped into the water . . . they could have been rescued. But we were told not to go out."

Oh Yong Seok, 58, a crew member who escaped with about a dozen others, including the captain, told the Associated Press that rescue efforts were hampered by the ferry's severe tilt.

"We couldn't even move one step," Oh said.

"We cannot give up," South Korean President Park Geun Hye said after a briefing in Seoul. "We have to do our best to rescue even one passenger."

White House spokesman Jay Carney said the United States and its Seventh Fleet stood ready to assist.

The last major ferry disaster in South Korea was in 1993, when 292 people were killed.

The water temperature was about 54 degrees Fahrenheit, cold enough to cause signs of hypothermia after about 11/2 hours, according to an emergency official.

Lee Gyeong Og, a vice minister for the Public Administration and Security Ministry, said the ocean was 121 feet deep in the area.

Survivors - wet, stunned, many without shoes - were taken to Jindo Island, where medical teams wrapped them in blankets and checked for injuries before taking them to a cavernous gym.

As the search dragged on, families of the missing gathered at a dock, some crying and holding each other. Boats circled the sunken ferry into the night, illuminated by red flares.

Angry shouts could be heard when Prime Minister Chung Hong Won visited a shelter where relatives of the missing waited for news. Some yelled that the government should have sent in more divers.

"If I could teach myself to dive, I would jump in the water and try to find my daughter," one parent, Park Yung Suk, said.

As frustration grew with the lack of information, some parents hired their own boat. "There was no rescue operation going on," said one father who declined to give his name. "I am extremely angry. Media is saying the rescue op is still going on. It's all a lie."

The Sewol, which travels twice a week between Incheon and Jeju, was built in Japan in 1994 and could carry a maximum of 921 people, 180 vehicles, and 152 shipping containers, according to Yonhap.

Of the 475 people on the ferry, there were 325 students and 15 teachers from Danwon High School in Ansan, near Seoul. They were headed to Jeju for a four-day trip.

Many Korean high schools organize trips for first- or second-year students, and Jeju is a popular destination. The students on the ferry were in their second year, which would make most of them 16 or 17.

At Danwon High, students were sent home early as parents gathered for news. Park Ji Hee, a first-year student, said she saw about a dozen parents crying at the school entrance.