Authorities investigating the passenger ferry grounding in waters off South Korea’s southwestern coast have placed the ship’s first mate and helmsman in emergency detention.

The Mokpo Coast Guard said on Thursday that the first mate and the helmsman, an Indonesian national, were taken into custody on suspicion of causing injury by gross negligence.

Investigators found that the first mate left the ship, the Queen Jenuvia II, on autopilot during a section of the route that required manual navigation of a narrow channel while he was searching for news on his mobile phone. 

As a result, the ship missed a key course change and ran aground on a rocky, uninhabited islet near Jangsan Island in Sinan County late Wednesday.

At the time of the accident, the ferry was traveling at 22 knots, or about 40-point-seven kilometers per hour, and had not made the speed reduction necessary to maneuver the channel. 

According to the Coast Guard, the first mate said in his initial statement that the steering wheel was not working correctly, but later admitted to investigators that he'd failed to change the ferry's course on time because he was looking at news on his phone.

The Coast Guard said that, though it is considering formally detaining the two suspects, it will continue to investigate the case, including conducting inspections of the grounded ship and calling in an interpreter to question the foreign crew member involved in the incident properly.

The ferry captain, who was out of the steering room and off duty at the time of the accident, is also under investigation.

The Queen Jenuvia II, carrying 246 passengers and 21 crew members, was en route to Mokpo when nearly half its hull ran aground on rocks at 8:16 p.m. on Wednesday. 

Thirty people who were injured when the ship made impact were later taken to nearby hospitals. No serious injuries were reported.