Norwegian authorities on Monday began investigating why a cruise ship was sailing in stormy weather when it developed engine trouble that triggered a perilous helicopter evacuation effort for hundreds of terrified passengers over the weekend.

“We don’t know the reason why the ship sailed, knowing such bad weather was forecast,” Kurt Olsen, acting director for Norway’s Accident Investigations Board, told USA TODAY. “We have a very good weather service in this country, so I would guess the crew knew everything about the forecast. How they responded will definitely be part of the investigation.”

Twenty-eight people were treated for injuries, according to Norwegian media, and nine remained hospitalized Monday, one critically.

The Viking Sky sailed from the northern city of Tromso bound for Stavanger in southern Norway when the ship began struggling with engine failure, started listing dangerously, then took in water. Norwegian media reported gusts up to 43 mph and waves over 26 feet. 

Cellphone footage from the ship shows furniture sliding across rooms as the boat rocks.

The crew issued a mayday call, and a team of helicopters airlifted almost 500 of the more than 900 passengers to safety Saturday night and Sunday morning. The ship, aided by tow vessels, finally limped into the Norwegian port of Molde on Sunday, freeing the remaining 436 passengers and crew of 458.

“The ship drifted to within 100 meters of running aground before they were able to restart one of the engines,” Hans Vik, chief of the Joint Rescue Coordination Center for southern Norway, told the nation’s TV2. “If they had run aground, we would have faced a major disaster.”

Olsen would not speculate why the Viking Sky captain decided to sail despite the weather warning. He said ship operations were one part of the investigation, along with a technical study of why the engines failed and a third review of how the rescue was handled.

“It’s really early in the investigation, so we just don’t know much yet,” Olsen said.

Yngve Skovly, a police inspector in the Molde region, told the Verdens Gang tabloid there was no suspicion of criminal behavior and the ship was too new to suspect maintenance problems. He said crucial information could be obtained from the ship’s computer logs.

Torstein Hagen, chairman of ship owner Viking Ocean Cruises, said his company would conduct its own investigation and support government agencies reviewing the mishap. Police expected all passengers to be flown out on Norway by Monday night. 

“The last few days have been both dramatic and hectic for guests and crew on board Viking Sky,” Hagen said in the statement. “I would like to apologize for all our guests have been through.”

The cruise had been scheduled to wrap up Tuesday in the British port of Tilbury on the River Thames. The passengers were mostly English-speaking, and many Americans were aboard.

Rodney Horgana said a huge wave crashed through the ship’s glass doors and swept his wife 30 feet across the floor.

“When the windows and door flew open and the 2 meters (6 feet) of water swept people and tables 20 to 30 feet, that was the breaker,” Horgan told the Associated Press. “I said to myself, ‘This is it.’ ”

Another American, Beth Clark, told Norwegian news outlet Dagbladet how she was plucked off the ship.

“The guy came down from the helicopter … snapped my belt and said, ‘Hold it,’ and shot me up about 100 feet in the air,” she said. Someone “grabbed me and pulled me in like a sack of potatoes and dragged me to the back of the helicopter.”

American Jan Terbruegn told Dagbladet there was little time for panic.

“We could see that we were getting blown in toward some rocks,” he said. “That was the most frightening thing, I think. But luckily, that wasn’t our destiny.”