MOKPO, South Korea (AP) — Strong currents and bad visibility hampered rescuers Thursday in the search for 289 passengers still missing more than 24 hours after their ferry flipped onto its side and filled with cold water off the southern coast of South Korea, causing fury among families waiting for word of passengers who were mostly high school students.

Seven were confirmed dead, but many expect that number will rise sharply because the missing have now spent more than a day either trapped in the ferry or in the cold seawater.

There were 475 people aboard 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 until only the blue-tipped, forward edge of the keel was visible.

Parents, siblings and other relatives of three high school students killed in the sinking wailed and sobbed as ambulances at a hospital in Mokpo took the students’ bodies to the city near Seoul where their high school is located. The families, who spent a mostly sleepless night at the hospital, followed the ambulances in their own cars.

The family of one of the victims, 24-year-old teacher Choi Hye-jung, spoke about a young woman who loved to boast of how her students would come to her office and give her hugs. She loved teaching and loved her students and was excited about her first-ever school trip to Jeju island. There were 325 students on board, headed to Jeju for a four-day trip.

“She was very active and wanted to be a good leader,” her father, Choi Jae-kyu, 53, said at Mokpo Jung-Ang Hospital while waiting for the arrival of his daughter’s body. Choi’s mother, sitting on a bench at the hospital, sobbed quietly with her head bent down on her knee.

Meanwhile, 20 divers tried to get inside the ship’s wreckage but couldn’t because of the current, the coast guard said. More than 400 rescuers searched nearby waters overnight and into Thursday morning.

Coast guard’s spokesman Cho Man-yong said Thursday that rescuers in a vessel had found another body floating in the sea, raising the confirmed death toll to seven. It was not immediately known whether the body was male or female. Besides the teacher, authorities said the dead included a female member of the crew and three male high school students. Details on the others were not immediately known.

Dozens were injured. Coast guard officials put the number of survivors early Thursday at 179.

It was still unknown why the ferry sank, but coast guard officials were interviewing the captain and crew. The Sewol, a 146-meter (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 to one side, according to the Ministry of Security and Public Administration.

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 that 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 Bon-hee, 36, told The Associated Press that 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 co-worker, said from a hospital bed in Mokpo 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, a 58-year-old crew member who escaped with about a dozen others, including the captain, told AP that rescue efforts were hampered by the ferry’s severe tilt. “We couldn’t even move one step. The slope was too big,” Oh said.

The Sewol’s wreckage is in waters a little north of Byeongpung Island, which is not far from the mainland and about 470 kilometers (290 miles) from Seoul.

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

White House spokesman Jay Carney said the U.S. and its 7th Fleet stood ready to assist, including the USS Bonhomme Richard, which was in the region.

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

TV stations broadcast live pictures Wednesday of the listing Sewol as passengers clambered over the side, jumped into the sea or were hoisted up by helicopters. At least 87 vessels and 18 aircraft swarmed around the stricken ferry.

The water temperature in the area was about 12 degrees Celsius (54 Fahrenheit), cold enough to cause signs of hypothermia after about 1½ hours of exposure, according to an emergency official who spoke on condition of anonymity because department rules did not allow talking to the media. Officials said the ocean was 37 meters (121 feet) deep in the area.

The survivors — wet, stunned and many without shoes — were brought to nearby Jindo Island, where medical teams wrapped them in pink blankets and checked for injuries before taking them to a cavernous gymnasium.

As the search dragged on, families of the missing gathered at a nearby 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 passengers waited for news. Some yelled that the government should have sent more divers to search the wreckage.

The numbers of passengers, as well as the dead and missing, fluctuated throughout the day. As of early Thursday, South Korean authorities estimated 475 people were on the ferry. Of that total, there were 325 students and 15 teachers from Danwon High School in Ansan, a city near Seoul, according to a relief team set up by Gyeonggi province.

Many South 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.

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 the Yonhap news agency.