A team of eight divers had entered a capsized South Korean ferry on Friday and was searching for survivors, although they were unlikely to find anyone alive from among hundreds still missing more than 48 hours after the vessel began sinking.

YTN television said that divers had searched the dining hall and cafeteria of the Sewol ferry, where many of the passengers, mostly high school students, were at the time of Wednesday's accident.

The ship is now fully submerged in waters about 25 km (15 miles) off the southwestern coast of South Korea.

Earlier in the day, investigators said that the 69-year old captain may not have been on the bridge at the time the vessel heeled sharply and then capsized.

"He (the captain) may have been off the bridge.. And the person at the helm at the time was the third officer," Park Jae-eok, an official investigating the accident, told a news conference in Mokpo, a city close to the port where rescue operations are being conducted.

It is normal for junior officers to take the helm and the 400 km (300 mile) journey from the mainland port of Incheon to the resort island of Jeju was a regular trip in familiar waters.

The official death toll for the ferry, which capsized on Wednesday carrying 475 passengers and crew, climbed to 25. A total of 179 have been rescued and many of the 271 still missing are children from one school on the outskirts of Seoul.

The accident happened in calm, shallow waters and investigators have focused on the role captain and the actions of the crew as the vessel appeared to have a clean safety record.

Parents of the missing schoolchildren blamed the ship's captain for the tragedy after he and shipping company officials made emotional apologies for the loss of life.

Witnesses have said that the captain and some of the crew left the vessel while others instructed passengers to remain in place as it began to sink.

Theories about the cause of the accident swirled and investigators declined to comment on reports the vessel had turned before it listed to port and capsized.

Coastguard officials have said the investigation was focused 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 captain, Lee Joon-seok, faces criminal investigation, which is standard procedure in South Korea.

Both 69-year-old Lee and the company that owns the ship have apologized for the loss of life, although neither has admitted responsibility.

Relatives were in mourning overnight in a hospital in the city of Mokpo, close to the port city of Jindo, which is acting as a rescue center. Some of them spoke bitterly of the captain.

"How could he tell those young kids to stay there and jump from the sinking ship himself?" said Ham Young-ho, grandfather of 17-year-old Lee Da-woon, one of the dead.

Lee has not made any public statement on whether or why he may have left the vessel before many of the passengers.