South Korea's coast guard says two people are dead and at least 290 missing after a passenger boat sank off the country's southern coast Wednesday.
The ferry was carrying more than 470 people, mostly students, to the resort island of Jeju when it sank in what appeared to be calm conditions.
Officials initially announced only around 100 people were unaccounted for. But they later drastically increased that number for unknown reasons.
Many could be trapped inside the almost completely submerged ship, though officials say some missing passengers may have been rescued by nearby commercial vessels.
South Korean Vice Minister of Security and Public Information Lee Gyeong-og said a massive rescue effort is under way.
A team of South Korean navy SEALS is also participating in the rescue.
The U.S. Navy said it is sending an amphibious assault ship, the USS Bonhome Richard, to join the search and rescue operation.
Most of the passengers were high school students headed to Jeju island on a school outing.