Survivors of a ferry that sank off South Korea's south coast earlier this week have shown serious symptoms of depression and anxiety, a hospital chief said Saturday.

A total of 29 passengers have been confirmed dead since the 6,825-ton ferry Sewol capsized and sank off the southwestern island of Jindo on Wednesday. More than 260 others remain unaccounted for, with most of them feared to be trapped inside the vessel.

Of the 174 survivors so far, 80 have been treated at the Korea University Ansan Hospital in Ansan, just south of Seoul, since they were rescued from the sinking ship.

"Based on our assessment of depression and anxiety levels, 16 patients with depression symptoms and 28 with anxiety symptoms have appeared to be at dangerous levels," Cha Sang-hoon, the head of the hospital, said in a press briefing.

“Symptoms of depression and anxiety can appear later, so we plan to keep a close eye on (the patients) even if they don't show any symptoms at the moment."

The hospital has expanded its team of specialists handling the passengers by requesting assistance from doctors at another hospital and assigned counselors to seven patients showing especially serious signs of depression, hospital officials said.

Students and other patients suffering from sleeping disorders have been put on medication, they added.

Starting Saturday, visits will be restricted to family members as much as possible in order to help keep the patients at rest.

Rescue operations have been under way for the fourth straight day, but progress has been slow due to strong currents and unfavorable weather conditions.

More than 300 of the 476 passengers were high school students from Ansan, who were on a school trip to the southern resort island of Jeju. (Yonhap)