COPENHAGEN, Denmark (AP) — A maritime official says the engines of a cruise ship failed off Norway's coast during a storm because they didn't have enough lubricating oil.

Lars Alvestad, the head of Norway's Maritime Authority, said Wednesday that low oil levels were the "direct cause" of the engine failure that stranded the Viking Sky on Saturday.

Alvestad says safety systems detected the problem and automatically stopped the engines to prevent a breakdown.

Viking Sky's crew sent a mayday call and anchored in heavy seas to keep the ship from being dashed on rocks in an area known for shipwrecks. Five helicopters lifted 479 passengers off with winches.

The rescue operation ended Sunday when the engines restarted. The ship traveled under its own power to a Norwegian port with nearly 900 passengers and crew members onboard.