Death toll in South Korea's ferry sinking disaster continued to rise to 171 on Thursday, but those recovered from the sunken ferry grew at a relatively slower pace as search operations were hampered by the unexpectedly swift currents.

The ninth day into search, 12 more bodies were retrieved from the submerged vessel Wednesday, raising the total death toll to 171. The number of missing was 131, with those rescued remaining fixed at 174.

On Wednesday alone, 38 bodies were discovered from the submerged vessel, with 36 people found Tuesday and 28 others retrieved on Monday.

Rescue operations were suspended for about six hours in the afternoon as tidal currents near the sunken vessel became faster than expected.

Some 40 family members of the victims visited the office of the government-wide disaster response headquarters at around 1 p.m. to protest against the sluggish rescue operations.

Weather forecast showed that tidal currents near Jindo Island, where the 6,825-ton ferry Sewol capsized and sank on April 16, would become slower for four days from Monday.

Divers were known to have begun plunging into the waters at about 3 p.m. to enter the vessel and search bodies, or possible survivors, believed to be trapped in passenger cabins on the third and fourth floors of the five-story ship.

Divers became fatigued due to the protracted underwater operations. One navy diver got decompression sickness while diving for a long time.

Around 700 coast guard, navy, special forces, firefighting and private divers were conducting search operations in the tough and murky waters, the coast guard said.