A South Korean ferry carrying 267 passengers and crew ran aground after the first officer got distracted by his mobile phone, the coast guard said.
The vessel crashed onto an uninhabited island off the country's southwestern coast.
All 246 passengers and 21 crew members were brought to safety and the ferry was towed to a port on Thursday. At least five of them had suffered minor injuries in the accident.
The incident occurred after 8pm local time on Wednesday as the vessel was sailing from the southern island of Jeju to the southwestern port city of Mokpo.
A mistake by the captain or a navigating officer might have caused the accident, but the coast guard will conduct a thorough investigation, the organisation's Commissioner General Kim Yong-jin said.
A coast guard official also told AFP that a preliminary investigation indicated that “the officer responsible for steering had been looking at his mobile phone and allowed autopilot to take control in an area where the ship should have been manually operated".
"As a result, the vessel missed the proper moment to change course, veered toward the uninhabited island and ran aground," the official told the French news agency.
Ships are normally steered manually, not using autopilot, in the area of the accident, a narrow sea channel surrounded by small islands near the shore, said Choi Jae Gon, an official from the Mokpo Coast Guard. "Because it is a narrow coastal area, it is a route that requires careful navigation," he said.
Authorities clarified that the crew members were not intoxicated.
A loud bang had startled passengers during the night, causing panic and confusion, said passenger Kim Namhyun.
"I thought I might die. The sound was too loud," said Kim, 51, a diving instructor on Jeju Island. "But having seen the Sewol ferry, I knew that in situations like this, you have to stay calm, move outside, wear a life jacket, and wait," said Kim, referring to the sinking of the Sewol ferry in 2014. Footage showed passengers wearing life vests awaiting transfer to rescue boats.
The coast guard is expected to press criminal charges against the helmsman due to the "clear negligence" that led to the vessel running aground.
The 26,500-tonne ferry appeared to have sustained damage to the bottom of its hull, according to video footage and photographs shared on social media.
In the wake of the accident, president Lee Jae Myung ordered "swift rescue efforts” to bring the passengers and the crew ashore and told officials to provide regular updates to the public.
The incident rekindled memories in South Korea of a 2014 ferry sinking that had killed more than 300 people dead. The wreck of that Sewol ferry was brought to Mokpo after almost three years.
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