Divers have plunged deeper into the submerged wreck of the South Korean ferry that sank more than a week ago as the death toll neared 160 and relatives of the 140-plus still missing pressed the government to finish the grim task of recovery.

At a port on Jindo island near the scene of divers' efforts, relatives lined up for a daily ritual, crowding around a large board to read updates about bodies found overnight and the search plan for the day. Volunteers posted messages of support. "Please come back home," one of the messages said. "We pray for you."

Navy divers are searching the rear of the ferry's fourth floor, officials posted on a board. The coastguard and a rescue company are searching the middle section of the same floor and another team is searching the front and middle of the fourth floor. Officials also posted new numbers at the port: 159 dead; 143 missing.

As divers go deeper into the ferry, the work gets harder as they find they have to rip through cabin walls to retrieve more victims. And looming in the background is the sensitive issue of when to bring in cranes and begin the salvage effort by cutting up and raising the submerged vessel.

"Now we think we have to deal with this realistically," said Pyun Yong-gi, whose 17-year-old daughter is among the missing.

"We don't want the bodies to decay further, so we want them to pull out the bodies as quickly as they can."

But that view is not shared among all relatives of the missing. One of them, Jang Jong-ryul, was sensitive about the mere mention of the word "salvage" and said most families do not want to think about it.

The number of corpses recovered has risen sharply since the weekend, when divers battling strong currents and low visibility were finally able to enter the submerged vessel. But the task is becoming more difficult.

"The lounge is one big open space, so once in it we got our search done straight away. But in the case of the cabins, we will have to break down the walls in between because they are all compartments," said Koh Myung-seok, the spokesman for the government-wide emergency task force.

The government has not said when it intends to begin the salvage effort, though it has said it will be considerate of the families of the missing.

For some relatives, speed in recovering the dead is becoming more important.

"I've seen the bodies and they are starting to smell. It inflicts a new wound for the parents to see the bodies decomposed," Mr Pyun said.

The victims of the April 16 disaster are overwhelmingly pupils of a high school in Ansan, near Seoul. More than three-quarters of the 323 students are dead or missing, while nearly two-thirds of the other 153 people on board survived.

Twenty-two of the 29 members of the ferry's crew survived, and 11, including Captain Lee Joon-seok, have been arrested or detained in connection with the investigation. Two of the crew were arrested yesterday.

Senior prosecutor Ahn Sang-don said an analysis of photos and video on the ship before its sinking showed the captain and other arrested crew members did not rescue passengers, though it was their duty. The crew members were at the ship's steering room or engine room together before fleeing the Sewol earlier than passengers.

The captain initially told passengers to stay in their cabins and waited about half an hour to issue an evacuation order. He has said he waited because the current was strong, the water was cold and passengers could have drifted away before help arrived.

But maritime experts said he could have ordered passengers to the deck - where they would have had a greater chance of survival - without telling them to abandon ship.

It was not the crew but a passenger who first alerted authorities that the boat was in distress, the coastguard said.

An emergency call was made 8.52am last Wednesday to the Jeonnam 119 fire department, which transferred the call to the Mokpo coastguard office, the coastguard said. The ferry made its first distress call three minutes later.

Yonhap news agency reported that the caller was a pupil from Ansan, and remains missing.

The cause of the disaster is not yet known and investigators are considering factors including wind, ocean currents, freight, modifications made to the ship and the fact that it turned just before it began listing.

A maritime professor who spoke to the Sewol's third mate, who is among those arrested and was steering the ferry before it sank, said he suspected a problem with the steering gear caused the sinking.

Kim Woo-Sook of Mokpo National Maritime University said he spoke to Park Han-gyeol, a former student, at a Mokpo detention centre. He said she told him she ordered a helmsman to make just a five-degree turn, but the steering gear turned too far and the helmsman could not turn it back.

Prof Kim said the steering gear would not have been enough alone to capsize the ship, but he suspected it caused poorly-secured freight to shift, making the vessel unbalanced.

He said he told her he believed she did not make any mistakes in steering the ship, but was wrong to have followed the captain in escaping the ship without protecting passengers.