All crew members of the sunken South Korean ferry are in custody

People hold candles at a vigil for students among the missing passengers of a South Korean capsized ferry in central Ansan on April 25, 2014.</p>

People hold candles at a vigil for students among the missing passengers of a South Korean capsized ferry in central Ansan on April 25, 2014.

All surviving crew members of a sunken South Korean ferry were in custody and under arrest Saturday, prosecutors said, as bad weather prevented the recovery of any of the more-than 100 bodies still missing.

The Sewol's captain, Lee Joon-Seok, and 10 crew members had already been arrested on charges ranging from criminal negligence to abandoning passengers.

The remaining four were arrested late Saturday after warrants were issued, prosecutors said.

The confirmed death toll from the tragedy stood Saturday at 187, with 115 unaccounted for — many bodies are believed trapped in the ferry that capsized on April 16 on a routine voyage to southern Jindo island with 476 people on board.

The ship's captain has been sharply criticized for delaying the evacuation order until the ferry was listing so badly that escape was almost impossible.

Prosecutors have raided a host of businesses affiliated with the ferry operator, the Chonghaejin Marine Company, as part of an overall probe into corrupt management.

The widening investigation has also seen travel bans put on eight current and former executives of the Korea Register of Shipping — the body responsible for issuing marine safety certificates.

A looming storm and high tides put a temporary halt to operations to recover the remains of those still missing over a week after the disaster.

Despite the difficult conditions, divers made several attempts to get into the ship, search officials said, but to no avail.

Frustrated families 

Making up the bulk of the passengers on the 6,825 ton Sewol when it sank were 325 high school students — around 250 of whom are either confirmed or presumed dead.

Although all hope of finding survivors has been extinguished, there is still anger and deep frustration among relatives of the missing over the pace of the recovery operation.

Frogmen have battled strong currents, poor visibility and blockages caused by floating furniture as they have tried to get inside the upturned vessel, which rests on a silty seabed.

The challenging conditions have meant divers are unable to spend more than a few minutes in the ship each time they go down.

Even so, they are coming across horrifying scenes in the murky water, including one dormitory room packed with the bodies of 48 students wearing lifejackets.

Around a quarter of the dead recovered so far have been found in waters outside the sunken vessel, and there are fears that some of the missing may have drifted free from the wreck.

That could be exacerbated if the sea is churned by the gathering storm, scattering bodies.

"As efforts to find the missing people are becoming protracted, there are growing concerns among their families that bodies might be lost for good," a coastguard official said.

Authorities — wary of the palpable anger among relatives — have mobilized trawlers and installed 13-kilometer-long (eight-mile-long) nets anchored to the seabed across the Maenggol sea channel to prevent the dead being swept into the open ocean.

Dozens of other vessels and helicopters have been scouring the site and beyond, with the search operation expanded up to 60 kilometres from the scene of the disaster.

Police and local government officials will also be mobilized to search coastal areas and nearby islands, a coastguard official said.

Dangerous conditions 

It took divers working in difficult and dangerous conditions more than two days to get into the sunken ferry and two more days to retrieve the first bodies.

Many relatives believe some of the victims may have survived for several days in trapped air pockets, but perished in the cold water after no rescue came.

As a result some have asked for autopsies to be performed, to see if it would be possible to determine the precise cause and time of death.

On Saturday, a US navy rescue and salvage vessel, the USS Safeguard, arrived at Jindo, AFP journalists on the scene said.

The vessel has "divers and other necessary equipment aboard, but it remains to be seen how the ship can contribute to the ongoing efforts to retrieve bodies," a US military spokesman told AFP.