Death toll rose to 273 on Friday in one of South Korea's deadliest maritime disasters as divers searched the sunken ferry amid slower tidal currents.

As of Friday morning, 273 people had been confirmed dead, and 31 others were still missing. No survivor had been reported since 172 people were saved from the ship and sea on April 16.

The 6,825-ton ferry Sewol capsized and sank off the country's southwestern coast 24 days ago. Two thirds of the 476 passengers were students and teachers from Danwon High School in Ansan, a city south of Seoul.

Koh Myung-seok, spokesman of the pan-government accident response center, told a press briefing that four more bodies were recovered from the submerged hull overnight, noting divers intensively searched cabins on the fourth and fifth floors of the five-story vessel where the remaining bodies were believed to be trapped.

The waters off Jindo Island, where the ship sank, have been into the period of neap tide, or the least difference between high and low tides, Koh said, noting diving conditions became better.

The area is famous for the nation's second-fastest tidal currents.

Divers completed the first-stage search into 64 passenger cabins, expanding their search range to 111 cabins and communal spaces such as restaurants and restrooms.

On Friday, 128 divers will continue to conduct search operations inside the submerged ship.