* Ship's captain arrested for alleged negligence
* Divers gain access to cargo deck
* Hopes fade for 274 people missing (Update with ferry captain arrested, paragraphs 13-15)
By Jungmin Jang and Ju-min Park
MOKPO/JINDO, South Korea, April 18 (Reuters) - The vice-principal of a South Korean high school who accompanied hundreds of pupils on a ferry that capsized has committed suicide, police said on Friday, as hopes faded of finding any of the 274 missing alive.
The Sewol, carrying 476 passengers and crew, capsized on Wednesday on a journey from the port of Incheon to the southern holiday island of Jeju.
Kang Min-gyu, 52, had been missing since Thursday. He appeared to have hanged himself with his belt from a tree outside a gym in the port city of Jindo where relatives of the people missing on the ship, mostly children from the school, were gathered.
Police said Kang did not leave a suicide note and that they had started looking for him after he was reported missing by a fellow teacher. He was rescued from the ferry after it capsized.
Twenty-eight people had been officially declared dead before Kang's suicide. One hundred and seventy-four were rescued. Most of the missing are students from the Danwon High School on the outskirts of Seoul, who were on a holiday trip.
The government revised the total number of passengers and the number of people rescued, saying there had been further inaccuracies in tabulation, without elaborating.
Divers are fighting strong tides and murky waters to get to the sunken ship. The likelihood of finding any of the missing alive is slim.
At the high school in Ansan, an industrial town near Seoul, many friends and family of the missing gathered in sombre silence, with occasional sounds of sobbing breaking the quiet.
"When I first received the call telling me the news, at that time I still had hope," said Cho Kyung-mi, who was waiting for news of her missing 16 year-old nephew at the school. "And now it's all gone."
In the classrooms of the missing, fellow students have left messages on desks, blackboards and windows, asking for the safe return of their missing friends.
"If I see you again, I'll tell you I love you, because I haven't said it to you enough," reads one message.
Investigations into the sinking, South Korea's worst maritime accident in 21 years based on possible casualties, have centred on possible crew negligence, problems with cargo stowage and structural defects of the vessel, although the ship appears to have passed all of its safety and insurance checks.
The ship's 69-year-old captain, was arrested early on Saturday, Yonhap news agency said, after coming under scrutiny over witness reports that he was among the first to escape the sinking vessel during its 400-km (300-mile) voyage to Jeju.
According to investigators, Captain Lee Joon-seok was not on the bridge at the time the Sewol started to list sharply, with a junior officer at the wheel.
Yonhap said Lee faced five charges including negligence of duty and violation of maritime law. Arrest warrants were also issued for the junior officer and one other crew member for failing in their duty to aid passengers.
"I'm not sure where the captain was before the accident. However, right after the accident, I saw him rushing back into the steering house ahead of me," said Oh Young-seok, one of the helmsmen on the ship who was off duty and resting at the time.
"He calmly asked by how much the ship was tilted, and tried to re-balance the ship," said Oh, who was speaking from a hospital bed in the city of Mokpo on Friday, where the injured have been taken.
Handing over the helm is normal practice on the voyage from Incheon to Jeju, which usually takes 13.5 hours, according to local shipping crew.
Divers gained access to the cargo deck of the ferry on Friday, although that was not close to the passenger quarters, according to a coastguard official.
Other coastguard officials said that divers made several attempts to reach the passenger areas but failed.
"We cannot even see the ship's white colour. Our people are just touching the hull with their hands," Kim Chun-il, a diver from Undine Marine Industries, told relatives of the missing.
The ferry went down in calm conditions and was following a frequently travelled route in familiar waters. Although relatively close to shore, the area was free of rocks and reefs.
Lee has not commented on when he left the ship, although he has apologised for the loss of life.
He was described as an industry veteran by the officials from Chonghaejin Marine Co Ltd, the ship owner, and others who had met him described him as an "expert".
"I don't know why he abandoned the ship like that," said Ju Hi-chun, a maritime author who interviewed the captain in 2006 as one of the experts on the route to Jeju island.
But he added: "Koreans don't have the view that they have to stay with their ship until the end. It is a different culture from the West."
Some media reports have said the vessel turned sharply, causing cargo to shift and the ship to list before capsizing.
Marine investigators and the coastguard have said it was too early to pinpoint a cause for the accident and declined to comment on the possibility of the cargo shifting.
The record of the ferry owner was also under investigation and documents were removed from its headquarters in Incheon.
Chonghaejin Marine Co Ltd is an unlisted company that operates five ships. It reported an operating loss of 785 million won ($756,000) last year.
According to data from South Korea's Financial Supervisory Service, a government body, Chonghaejin is "indirectly" owned by two sons of the owner of a former shipping company called Semo Marine which went bankrupt in 1997. (Additional reporting by Jack Kim, Miyoung Kim, James Pearson, Sohee Kim and Cho Meeyoung; Writing by David Chance; Editing by Raju Gopalakrishnan and Nick Macfie/Mark Heinrich)