Divers battled strong currents and near zero visibility today to finally enter a South Korean ferry two days after it sank, as investigators sought arrest warrants against the captain and two crewmen.

The breakthrough by dive teams came more than 48 hours after the 6,825-tonne Sewol capsized -- a delay that has incensed the relatives of the 268 people still missing from the disaster.

The unfolding tragedy was compounded by the apparent suicide of a high school vice principal who had been rescued from the 6,825-tonne Sewol that sank Wednesday morning with hundreds of his students trapped inside.

After several attempts, two divers managed to pry open a door and enter the cargo section on Friday afternoon, a senior coastguard official said.

Hours later another two-man team accessed one of the cabins, but found nothing."The search operation will continue through the night," the official said.

The confirmed death toll stood at 28, but the focus of concern remained on the 268 still unaccounted for and slim hopes that some may have survived in air pockets in the submerged vessel.

"Visibility is almost non-existent. You can hardly see your hand in front of you face," said one diver when he returned to the harbour at nearby Jindo island.

The coastguard said a joint investigation team of police and prosecutors had applied for arrest warrants for captain Lee Joon-Seok, 52, and two crew.

The charges were not specified.

Earlier, prosecutors said preliminary investigations showed Lee had handed the helm to his third officer before the ferry capsized.

Of the 475 people on board when the Sewol capsized, only 179 were rescued and no new survivors have been found since Wednesday.

Three giant, floating cranes reached the rescue site, but regional coastguard commander Kim Soo-Hyun stressed they would not begin lifting the multi-deck ferry until they were sure there were no survivors inside.

"I want to be clear: There won't be any salvage work done against the will of the families," Kim aid.

More than 350 of those on board were from the Danwon High School in Ansan city just south of Seoul.