Prosecutors in South Korea have asked a court to issue an arrest warrant for the captain of the ferry that sank on Wednesday, officials say.
It was earlier revealed that a junior officer – and not the captain – was at the helm of the ferry when it capsized.
Efforts to find the 268 people still missing have been hampered by low visibility and strong currents.
Twenty-eight people are now known to have died in the disaster, with 179 people rescued.
Coast guard officials said on Friday two divers managed to enter the cargo bay of the vessel, but could not identify or rescue anyone due to items obstructing the way.
The vessel – named Sewol – had been travelling from Incheon, in the north-west, to the southern resort island of Jeju. It capsized and sank within a period of two hours, officials said.
Some 350 of those on board were students from Danwon High School in Ansan, a suburb of Seoul, who were on an outing when the ferry sank.
Investigations are focusing on the sharp turn the vessel took before it started listing and whether an evacuation order by the captain could have saved lives.
Some experts believe such a tight turn could have dislodged heavy cargo and destabilised the vessel, while others suggest it could have been caused by a collision with a rock.
In addition to the captain, arrest warrants are also being sought for two other crew members, reports say.
“The joint investigation team of police and prosecutors asked for warrants to arrest three crew, including the captain,” a coast guard official in Makpo told AFP.
Captain Lee Joon-seok, who has already been quizzed by police, was shown on television on Thursday apologising to the victims and their relatives.
“I am really sorry and deeply ashamed. I don’t know what to say,” he said.
Details of the charges have not yet been made public.
The vice principal of Danwon High School, who was rescued from the ferry, was found dead on nearby Jindo island on Friday.
Kang Min-Kyu, 52, had been missing since Thursday and was discovered hanging from a tree near the gym on Jindo island – where many of the relatives of missing passengers have been staying.