The resignation offer comes amid rising indignation over claims by the victims' relatives that the government didn't do enough to rescue or to protect their loved ones. Most of the missing and dead were high school students on a school trip. Officials have taken into custody all 15 people involved in navigating the ferry that sank April 16, a prosecutor said.
South Korean executive power is largely concentrated in the president, Park Geun-hye, so the resignation offer by Prime Minister Chung Hong-won appears to be largely symbolic. There was no immediate word from Park about whether she would accept Chung's resignation.
Chung was heckled by relatives and his car was blocked when he visited a shelter on an island near the site of the sinking a week ago. On Sunday, he issued an extraordinary statement to reporters in Seoul on the national tragedy.
"As I saw grieving families suffering with the pain of losing their loved ones and the sadness and resentment of the public, I thought I should take all responsibility as prime minister," Chung said. "There have been so many varieties of irregularities that have continued in every corner of our society and practices that have gone wrong. I hope these deep-rooted evils get corrected this time and this kind of accident never happens again."
Meanwhile, Yang Jung-jin of the joint investigation team said two helmsmen and two members of the steering crew were taken in on preliminary arrest warrants issued late Friday. Formal arrest warrants were issued Saturday night. Eleven other crew members, including the captain, had been formally arrested earlier.
All are accused of negligence and of failing to help passengers in need as the ferry Sewol sank. The captain initially told passengers to stay in their rooms and took half an hour to issue an evacuation order, by which time the ship was tilting too severely for many people to get out.
Divers have recovered 187 bodies and 115 people are believed to be missing, though the government-wide emergency task force has said the ship's passengers list could be inaccurate. Only 174 people survived, including 22 of the 29 crew members.
The seven surviving crew members who have not been arrested or detained held non-marine jobs such as chef or steward, Yang said in a telephone interview from Mokpo, the southern city near the wreck site where prosecutors are based.
South Korean television aired video of police escorting the four men to court. All four wore baseball caps that hid their faces, and at least one was limping.
Capt. Lee Joon-seok told reporters after his arrest that he withheld the evacuation order because rescuers had yet to arrive and he feared for passengers' safety in the cold water. Crew members have also defended their actions.
Helmsman Oh Yong-seok, one of those arrested Saturday, has said he and several crew members did their best to save people. He said that he and four crew members worked from nearby boats to smash windows on the sinking ferry, dragging six passengers stuck in cabins to safety.
Officials in charge of the search effort said divers had reached two large rooms where many of the lost may lie dead, but the search has been suspended since Saturday because of bad weather. Currents were also strong, as they were in the first several days of the search, when divers struggled in vain even to get inside the submerged vessel.
The two rooms where searchers hope to find more of the missing soon are sleeping units designed for many people - one in the stern and one in the bow. Fifty students from Danwon High School in Ansan were booked into one of them. Students from the city near Seoul make up more than 80 percent of the dead and missing; they had been on their way to the southern tourist island of Jeju.
Large objects that toppled when the ferry tipped over and sank are believed to be keeping divers from reaching bodies in at least one of the rooms.
The Ministry of Oceans and Fisheries also said it would soon change ferry systems so that passenger, vehicle and cargo information is processed electronically. There is not only uncertainty about how many people were on the Sewol, but a huge discrepancy regarding the amount of cargo it was carrying when it sank.
The Sewol was carrying an estimated 3,608 tons of cargo, according to an executive of the company that loaded it. That far exceeds what the captain claimed in paperwork - 150 cars and 657 tons of other cargo, according to the coast guard - and is more than three times what an inspector who examined the vessel during a redesign last year said it could safely carry.
Yang, the prosecutor, said that the cause of the sinking could be due to excessive veering, improper stowage of cargo, modifications made to the ship and tidal influence. He said investigators would determine the cause by consulting with experts and using simulations.