Homicide conviction: Lee Joon-seok, the captain of the sunken South Korean ferry Sewol, arrives for verdicts at Gwangju High Court in Gwangju, South Korea . The South Korean ferry captain responsible for a sinking that killed more than 300 people has had his sentence increased to life in prison. Lee Joon-seok had been ordered to serve 36 years in prison for negligence and abandoning passengers aboard the Sewol, by a district court following last year's disaster. But this was increased to life in prison today by an appellate court that convicted him of homicide by account of his 'willful negligence'. The 6,825-tonne passenger ship sank off the southwest coast on April 16 last year, killing 304 people. Most of the victims were teenagers who were en route to a southern island for a school trip. Victims' relatives criticised the original verdict which had acquitted him of homicide, saying it was too lenient. But his sentence was increased because the Gwangju High Court additionally convicted him on the homicide charges while upholding most of other charges that led to his November conviction, according to a court statement. The appellate court sentenced 14 other navigation crew members to 18 months to 12 years in prison, the statement said. In November they had received sentences of five to 30 years in prison. The court said it decided on Lee's homicide conviction 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. Lee's behavior was 'homicide by willful negligence,' the court judged. 'For whatever excuses, it's difficult to forgive Lee Joon-seok's action that caused a big tragedy,' the court statement cited the verdict as saying. Lee and the 14 crew members have been the subject of fierce public anger because they were among the first people rescued from the ship when it began badly listing on the day of the sinking in April last year. Scroll down for video . Disaster: Helicopters try to help passengers stranged on the South Korean ferry which sank on its way to Jeju island from Incheon, some 20 kilometres off the island of Byungpoong in Jindo, South Korea . Devastating: A girl is rescued from the stricken vessel while relatives grieve for the victims of the 2014 Sewol ferry disaster, whose captain has today been jailed for life . Lee has said he issued an evacuation order, but the court statement said two of the 14 crew members acknowledged that there was no evacuation order. Many student survivors have said they were repeatedly ordered over a loudspeaker to stay on the sinking ship and that they didn't remember there any evacuation orders made by crew members before they helped each other to flee the ship. Judges sit to preside over verdicts for the sunken South Korean ferry Sewol's crew members who are charged with negligence and abandonment of passengers in the disaster at Gwangju High Court in Gwangju . Court spokesman Jeon Ilho said both prosecutors and the crew members have one week to appeal the verdicts. Lee Joon-seok, the captain of the sunken South Korean ferry Sewol, was sentenced to life in prison . A year after sinking, 295 bodies have been retrieved but nine others are missing. There is still lingering public criticism against the government over its handling of the sinking, the country's deadliest maritime disaster in decades. Violence occurred during a Seoul rally led by relatives and their supporters earlier this month, leaving dozens of people injured. Last week, South Korea formally announced it would salvage the ship from the ocean floor off the country's southwest coast. Relatives of the victims hope that might locate the missing, including four students, and help reveal more details about the sinking. Some experts are skeptical about those wishes and remain opposed to spending taxpayer's money to lift the civilian vessel. Officials say the salvage job is estimated to cost £68 million and take 12 to 18 months. Authorities blame excessive cargo, improper storage, botched negligence and other negligence for the sinking, and have arrested about 140 people. Critics say higher-level officials haven't been accountable.
Lee Joon-seok had sentence extended from 36 years to life in jail .
Judge ruled his actions were 'homicide by willful negligence'
He was one of the first rescued and never ordered evacuation .
Most victims of the Sewol disaster were high school students .
Follows protests from victims families who are calling for ship to be raised .