South Korea's highest court on Thursday sentenced the head of a ferry operator to seven years in prison over a ship sinking last year that killed more than 300 people.

The Supreme Court upheld a lower court ruling that sentenced Kim Han-sik, president of Chonghaejin Marine Co., to seven years in prison on charges including manslaughter. The court found Kim responsible for failing to prevent the overloading of cargo and improper storage on the ship that judges said contributed to the sinking.

Four other Chonghaejin officials were sentenced to two-and-a-half to four years in prison on similar charges, the court said in a statement.

A total of 304 people died when the ferry Sewol sank off South Korea's southwest coast in April 2014 in one of the country's deadliest maritime disaster in decades. Most of the victims were teenagers from a single high school.

Divers recovered 295 bodies from the wreckage before the government stopped underwater searches last year. Nine victims remain missing.

The Supreme Court couldn't confirm when it will be able to make a verdict on Sewol captain Lee Joon-seok, who appealed after a regional high court convicted him of homicide and sentenced him to life in prison in April.

The Gwangju High Court ruled that Lee committed "homicide by willful negligence" because he fled the ship without making any evacuation order, though he, as a captain, is required by law to take some measures to rescue his passengers.

South Korea is now paying $74 million to a consortium led by China's state-run Shanghai Salvage Co. to handle the difficult and potentially dangerous operation of salvaging the 6,800-ton Sewol. The government expects the ship to be raised by around July next year.

The relatives of the ferry victims hope that raising the ship will reveal details about the cause of the sinking and help find the bodies of nine passengers still missing.