The civilian diver died in hospital on Tuesday after losing communication about five minutes into the underwater search, authorities said. He had been diving to fix guideline ropes on the fifth deck of the Sewol ferry.

The vessel sank off South Korea's southwestern coast en route to Jeju island on April 16, carrying 476 passengers - 339 of whom were school children. The confirmed death toll so far stands at more than 260, with up to 40 still missing. Only 174 survived the disaster.

The man is the first fatality among divers tasked with helping in the search efforts, which are continuing despite the death. Authorities believe that most of the remaining missing people are in 64 of the ship's 111 areas.

Government spokesman Ko Myung-seok said divers have searched all 64 areas and plan to do so again. Divers entered the last three unopened areas on Monday night, Ko said, but have been hampered by dangerous conditions - such as darkness, floating debris and a maze of corridors and cabins.

So far, 19 people have been arrested in the investigation - 15 of them crew members accused of abandoning passengers. An executive from the company that owns the ferry has also been detained.

Last week, three people not on board the vessel were arrested, suspected of negligence in the handling of cargo on the ferry. Overloading of cargo and improper stowage are seen as possible reasons for the sinking.

Grief and growing anger over the government's handling of the disaster has seen the South Korean prime minister resign, and repeated criticism from President Park Geun-hye of the role played by government officials and the ferry operator.

President Park has promised to improve national safety policies to ensure better adherence. But her approval rating has dropped 12 points to 53 per cent, according to Seoul pollsters Realmeter.

jr/kms (Reuters, dpa, AP)