Desperate search and rescue efforts for hundreds still unaccounted for in a deadly ferry accident in waters off South Korea's southwestern coast continued for a fourth day on Saturday, with the whole country clinging to dim hope of finding survivors.

Hundreds of Navy and Coast Guard officers, along with civilian divers, have been battling strong underwater currents and low visibility to reach 273 people believed to be trapped inside the ferry Sewol that sank three days ago.

More than 72 hours have passed since the 6,825-ton ship sank off the southwestern island of Jindo on a foggy Wednesday morning.

A total of 476 passengers, including 325 high schoolers on a field trip, were aboard the ship en route to the southern resort island of Jeju from the western port of Incheon.

As of 10 a.m., 29 passengers had been confirmed dead. While 174 have been rescued, no one has been found alive since around Wednesday noon when the ship went under.

"We've yet to get any response from survivors underwater.

Divers have continued all-out operations to enter cabins, while pumping air to help them breathe," Coast Guard officer Choi Sang-hwan said.

Experts say people could possibly survive for 72 hours if there are air pockets in the compartments.

"Instead of dispatching two divers at a time, we are to send up to 10 workers at the same time to speed up the job We are working to install more guide lines" he said, referring to lines that help workers move inside vessels.

During overnight operations, divers found three dead bodies wearing life jackets inside the cabin on the fourth floor of the five-story ferry, officers said, adding they are trying to break the window to recover them.

"As weather conditions are forecast to worsen in the afternoon, we will do everything to make progress in the morning," Choi added. (Yonhap)