Seven U.S. Navy sailors are missing off the coast of Japan after an Aegis guided-missile destroyer, the USS Fitzgerald, collided with a container ship early Saturday, causing significant damage and flooding.

Three of the Fitzgerald’s crew members, including its commanding officer, Cmdr. Bryce Benson, were evacuated from the damaged vessel and are being treated at the U.S. naval hospital at Yokosuka, the home of the Navy’s Seventh Fleet.

Benson was reported to be in stable condition in the hospital, while the other two were still having their injuries assessed. The Seventh Fleet had set up an information center for families of sailors serving on the ship.

The cause of the collision was not yet clear.

“Right now we are focused on two things: the safety of the ship and the well-being of the sailors,” said Adm. Scott Swift, commander of the U.S. Pacific Fleet. 

The U.S. Navy destroyer USS Fitzgerald suffered damage when it collided with a Philippine-flagged merchant ship off Shimoda, Shizuoka prefecture, Japan, on June 17, 2017. (Iori Sagisawa/AP)

The USS Dewey, another destroyer, and two naval tugboats were at the scene, about 12 miles from the Izu Peninsula and 56 nautical miles southwest of Yokosuka, searching for the missing sailors on Saturday. Two Japanese coast guard cutters with helicopters were helping. The Fitzgerald returned to Yokosuka Naval Base.

The Fitzgerald, which is more than 500 feet long, collided with a fully laden, Philippine-flagged container ship, the ACX Crystal, about 2:30 a.m. local time.

The Crystal is about 700 feet long and was bound for Tokyo, according to a website that tracks maritime traffic.

Local broadcaster NHK showed helicopter footage of the container ship with minor damage to its bow, while the Fitzgerald appeared to have significant damage above and below the waterline. Water was being pumped from the destroyer.

The Fitzgerald is part of the Yokosuka-based group that includes the aircraft carrier USS Ronald Reagan, but it was operating independently of the carrier when the collision occurred, Flanders said.

The Fitzgerald was operating under its own power after the collision, but was making less than 1 to 3 mph.

When its crew is at full strength, the Fitzgerald usually has more than 250 personnel aboard and can reach speeds well over 30 miles per hour. It is unclear how fast the destroyer was traveling when it and the merchant ship collided.

Also unclear was how the two massive vessels collided.

There are extensive international guidelines for accident avoidance at sea known as the International Regulations for Preventing Collisions at Sea, or Colregs. 

The rules require that ships must have a watch posted at all times and follow a number of collision-avoidance steps when crossing paths with or overtaking other vessels.

Gibbons-Neff reported from Washington.