been caught. more now on our top story, authorities in south korea are trying to figure out what caused that passenger ship to sink in the waters of the country's southwest coast. >> yeah, close to 300 people are still unaccounted for. and a massive rescue operation is in full swing, amara walker reports. >> reporter: this is the ferry sewol, now almost completely submerged. the ship headed towards jeju, nearly 500 people on board, 325 of them high school students from just outside seoul on a class trip. wednesday, shortly before 9:00 a.m., the ship sent out a distress call. witnesses heard a loud bang, then the ferry started to list. the passengers were urged to put on their life jackets, and the passengers began to scramble. >> there was an announcement telling us to sit still on the