A port official said he was told the North Sea collision produced "a massive fireball" and the cargo ship's owner said one crew member was missing.

The captain of the Solong cargo ship who was arrested after crashing into an oil tanker off the English coast is a Russian national, the vessel’s owner said Wednesday, as maritime experts search for answers.

U.S.-based maritime management firm Crowley, which operates the Stena Immaculate, said the tanker “sustained a ruptured cargo tank containing Jet-A1 fuel,” when the container ship struck it, triggering a fire and “multiple explosions onboard,” with fuel released into the sea. It said all 23 mariners on the tanker were safe and accounted for.