SEOUL (AFP) - A probe into South Korea's ferry disaster has heard that warnings over the ship's seaworthiness were ignored, prosecutors said on Wednesday, as rescuers worked to recover more than 90 people still missing two weeks after it sank.

The confirmed death toll from the accident stood at 210, with 92 unaccounted for, the coast guard said, with divers pushing deeper into the submerged vessel's interior in their search for bodies.

Prosecutors investigating the disaster on Tuesday questioned the regular captain of the 6,825-tonne Sewol, who was on leave when it capsized on April 16 with 476 people on board - most of them high-school students.

Senior Prosecutor Yang Jong Jin said the captain, identified only with a surname Shin, told investigators that he had warned the shipping company of serious stability problems with the Sewol.

The Chonghaejin Marine Co. purchased the then 18-year-old ferry from Japan in 2012 and refurbished it, building extra passenger cabins on the third, fourth and fifth decks.

Capt Shin said the renovations altered the balance of the ship and undermined its anti-rolling ability.

When he advised the company about the problems, his warnings were brushed aside, he told investigators.

The precise cause of the accident is still under investigation, but experts have suggested a sharp turn may have caused its cargo to shift, and the ferry to list irretrievably to one side before capsizing.

The recovery operation has stalled in recent days because of strong currents and debris blocking access to some of the cabin decks.

Mr Kim Han Sik, the chief executive of Chonghaejin Marine, was summoned to the prosecutors' office on Tuesday in the port city of Incheon, from where the ill-fated ferry departed bound for Jeju Island.

Mr Kim, 71, issued a tearful apology for the "horrible tragedy" the day after the accident, saying he and other company officials were responsible for a "grave sin" in letting it happen.

In Capt Shin's absence, the Sewol was skippered by Captain Lee Joon Seok, who is now under arrest along with 14 crew members.

The coast guard released a video earlier this week showing Lee scrambling to safety as hundreds of his passengers remained trapped inside the ferry.

Public disgust at the behaviour of the crew has been matched by the anger of the victims' relatives with the official response to the disaster.

President Park Geun Hye apologised on Tuesday for her government's failure to combat systemic and regulatory "evils" that may have contributed to the accident and for the "insufficient first response". But many of the victims' families rejected her apology, which was made during a meeting with her Cabinet ministers.

"An apology made before several Cabinet members behind closed doors cannot be considered an apology," said Mr Yoo Gyeong Geun, the spokesman for a group of around 100 families who issued a statement demanding a thorough probe into the rescue operation.

The tragedy has proved a challenge for Ms Park, who has built a reputation for strong leadership since taking office just over a year ago, but is sometimes criticised for being aloof and domineering.

On Tuesday, Ms Park visited a memorial to the young victims of the disaster in Ansan city, where the high school that had 325 students on board the Sewol is located.

She was heckled during her visit by some family members who also turned away wreaths donated by the President and other senior officials.