SEOUL: South Korea on Monday recognised three people who died saving others in last month's ferry capsize as national "martyrs" -- lending a heroic chapter to a disaster narrative dominated by accusations of cowardice, corruption and incompetence.

All three were part-time crew members, including an engaged couple -- Kim Ki-woong and Jung Hyun-seon -- who could have escaped the sinking vessel but stayed to help trapped passengers.

The third was Park Ji-young, 21, the youngest crew member, who became a public hero after it emerged that she had given her life jacket to a passenger as she sought to guide people to safety.

Being designated martyrs entitles them to burial at a national cemetery, and their families will be eligible for financial compensation, medical assistance and other incentives.

The behaviour of the part-timers stood in stark contrast to the captain and most of the crew who were among the first to abandon ship and have been widely vilified for leaving trapped passengers to die.

All 15 surviving crew members, including the captain, have been arrested.

The confirmed death toll from the disaster stood at 275 on Monday, with 29 still unaccounted for as dangerous conditions suspended recovery operations for a third straight day.

The 6,825-tonne ferry Sewol capsized and sank off the southern coast on April 16.

Divers have been unable to access the submerged vessel since Saturday morning, with strong tides and heavy swells pushing conditions beyond the safety limit.

There is intense pressure on the recovery teams to wrap up the grim task of pulling every body from the ferry as soon as possible.

The families of those still missing oppose raising the vessel until every body has been retrieved.

But the search, in near-zero visibility, is becoming increasingly dangerous, with some partition walls on the ship warping and at risk of collapse.

"We will put the priority on the safety of divers when they search through dangerous areas," coastguard spokesman Ko Myung-Suk told a daily briefing.

The Sewol was carrying 476 people when it sank after listing sharply to one side and then rolling over.

Of those on board, 325 were children from a high school on an organised trip to the southern resort island of Jeju.

Initial investigations suggest the ferry was carrying up to three times its safe cargo capacity.

The Sewol's regular captain, who was off duty on the day of the accident, has told prosecutors that the ferry operator -- Chonghaejin Marine Co -- "brushed aside" repeated warnings that the 20-year-old ship had stability issues following a renovation in 2012.

Five Chonghaejin officials, including the company's head, have been arrested on various charges including manslaughter, negligence and breaches of safety regulations.