Crew members detained over South Korea's ferry disaster have said  they had done their best to launch life rafts, and one suggested possible technical reasons for the ship capsizing.

The four crew members were taken into police custody on Monday, and were paraded, heads bowed and hiding their faces, before TV cameras on Tuesday.

"We tried to gain access to the rafts but the whole ship was already tilted too much", one crew member said when asked why only one of the Sewol's 46 life rafts had been used. 

"We tried to launch the life rafts but it was hard to get to where they were," another said.

The 6,825-tonne Sewol had 29 crew, including its captain Lee Jeon-Sook.

Twenty of them escaped the ferry as it sank last Wednesday morning, and there has been public outrage at reports they were among the first to evacuate while hundreds remained trapped in the vessel.

One crew member, apparently an officer, suggested the ferry had a structural flaw that made it difficult to regain equilibrium once it had been lost.

The ship was built in 1994 in Japan and purchased by the Cheonghaejin Marine Company in 2012.

The officer also mentioned "some errors" with the steering system. The Sewol capsized after making a sharp right turn.

This led experts to suggest its cargo manifest might have shifted, causing it to list beyond a critical point of return.

Lee and two crew members were arrested over the weekend and charged with criminal negligence, before the arrests on Monday. 

The official death toll stood at 108 Tuesday, with 194 still missing. Most of the passengers were high school students on a holiday trip.  

Source: AFP