The two were at the helm of the vessel and are suspected of waiting too long to override the autopilot, allowing the ship to run into an uninhabited island in a busy passage approaching the southwestern port of Mokpo, the coast guard officers said.

The 26,546-tonne ship, with a passenger capacity of 1,010 and multiple decks for cargo and passenger vehicles, ran aground as it approached Mokpo from the southern island of Jeju but remained upright as all 267 people on board were rescued.

The incident rekindled memories in South Korea of the 2014 Sewol ferry disaster that killed more than 300 people, many of whom were children on a school trip. The Sewol sank in the same area but further out to sea.

A coast guard investigator in Mokpo told a briefing that the crew members in the latest incident had given conflicting testimony.

"Whatever their testimonies so far, we're looking at gross negligence," Kim Hwang-gyun said.

In initial testimony, the first officer said he was watching news on his phone at the time of the incident.

Kim said the investigation would include a forensic examination of the crew members' phones, the ferry's navigation data and vessel traffic control in the area.

The operator of the ferry, Seaworld, did not answer telephone calls seeking comment at its Mokpo office.

Several people received medical attention but no lives were in danger and the ferrysustained minor damage to the hull, other coast guard officials have said.

The vessel did not veer off course and was sailing at 22 knots (40 kilometers per hour) within regulation when it failed to make a turn, Kim, the coast guard investigator, said.

Authorities will examine whether the ship was unable to change course in time in the area's narrow navigation channels.

Ships are usually steered manually, rather than with autopilot, in the area, a narrow sea channel surrounded by small islands near the shore, according to another coast guard official.

"Because it is a narrow coastal area, it is a route that requires careful navigation," Choi Jae-gon said earlier.

The crew members were not intoxicated, officials said.

The ferry was towed to Mokpo port with its steel surface crumpled and scratch marks on the hull, according to photographs presented by the coast guard.

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