On April 16, there were 476 people known to be on board SEWOL. According to reports, 339 of these people were high school students from Danwon High School in Ansan, which is not too far from Seoul, along with some of their teachers. The rest of the people were passengers on other business, and crew.
About 16 miles from shore off the southern tip of South Korea, shortly before 9:00 a.m. KST, in calm weather, SEWOL made a hard turn and began to list. Minutes later, a loud noise reverberated. Whilst most of the passengers obeyed the captain's instructions to remain in their quarters, SEWOL listed ever farther to port, eventually to a degree which removed all hope of evacuating those passengers.
By the time the captain made the call to abandon ship, about an half-hour after that hard turn, the intercom system no longer functioned. Good Samaritans in the area and arriving rescue workers saved as many people as they could find, as the SEWOL beam listed perpendicular to the sea, trapping students and other passengers inside. SEWOL took over three hours to sink completely into seas where SAR divers report visibility to be mere inches in front of their faces.