The South Korean authorities have arrested four more crew members from the ferry that sank last week, bringing the total number detained to 11.

Police have also raided offices of companies linked to the ferry's owners.

Search teams are continuing to recover bodies from the submerged hull of the passenger ferry.

One survivor has described taking the agonising decision to save himself as the ship capsized and water washed away students he was trying to rescue.

The number of people known to have died in the accident has reached 150, with another 152 still missing, most of them teenage children from a single school in Ansan, outside the capital Seoul.

An emotional memorial service took place near the school on Wednesday, with friends and family members laying flowers in front of photographs of some of those who died.

The government is under strong public pressure to find out why the ferry capsized.

Twenty-two of the 29 members of the ferry's crew survived and prosecutors say the 11 arrested were on the bridge when the ship listed and sank within two hours of distress signals being sent.

The BBC's Jonathan Head on the island of Jindo, where the recovery operation is being co-ordinated, says authorities are moving quickly against those they blame for the disaster.