(Bloomberg) — South Korea's government said 284 people are missing after a ferry carrying hundreds of high school students sank en route to the resort island of Jeju, in what may be the nation's worst ferry accident in two decades.

At least four people, including a student, died in the accident, which occurred off the southwest corner of the Korean peninsula yesterday, Korea Coast Guard said in an e-mailed statement. Of the 462 passengers and crew, 174 people have been rescued including 75 students and two teachers. The government earlier said 368 people were rescued, a mistake it said was caused by double-counting.

The passengers included 325 students and 14 teachers from Danwon High School on an excursion to Jeju island, according to the school's website. A board posted at the school used to track those rescued showed that only 80 had been accounted for. They were in their penultimate year of high school at Danwon, which has 1,376 students.