The Japanese coast guard also said the US ship was experiencing some flooding but was not in danger of sinking.
Tokyo: Seven crew members are missing and at least three injured after a US Navy destroyer collided early on Saturday morning with a Philippine-flagged merchant vessel south of Tokyo Bay in Japan, the US Navy said.
The Japanese Coast Guard said the US ship was experiencing some flooding but was not in danger of sinking, while the merchant vessel was able to sail under its own power.
The US Navy said in a statement the USS Fitzgerald collided with a merchant vessel at about 2:30 a.m. local time (1730 GMT), some 56 nautical miles southwest of Yokosuka, a rare incident on a busy waterway.
Three aboard the destroyer had been medically evacuated, including the ship's commanding officer, Cmdr. Bryce Benson, who was reportedly in stable condition after being airlifted to the US Naval Hospital in Yokosuka, the Navy said.
The other two injured were transferred to the hospital for lacerations and bruises, while other injuries were being assessed, it said. The Fitzgerald and the Japanese Coast Guard were searching for seven missing sailors.
"The USS Fitzgerald suffered damage on her starboard side above and below the waterline," the Navy said in a statement.
It said the full extent of damage to the ship and injuries to its crew were still being determined. The Fitzgerald was operating under its own power, "although her propulsion is limited".
A spokesman for the US 7th Fleet said the ship was heading back to Yokosuka under its own power at 3 knots.
It was unclear how the collision happened. "Once an investigation is complete then any legal issues can be addressed," the 7th Fleet spokesman said.
The waterways approaching Tokyo Bay are busy with commercial vessels sailing to and from Japan’s two biggest container ports in Tokyo and Yokohama.
The USS Dewey and two Navy tugboats had been dispatched to provide assistance, the Navy said.
Japan's public broadcaster NHK showed aerial footage of the destroyer, which had a large dent in its right, or starboard, side. Images broadcast by NHK showed it had been struck next to its Aegis radar arrays behind its vertical launch tubes.
The images showed what appeared to be significant damage on the deck and to part of the radar. NHK also showed footage of the container vessel and said it was heading towards Tokyo under its own power.
The 7th fleet said the collision was with the Philippine-flagged merchant vessel ACX Crystal. At around 29,000 tons displacement it is about three times the size of the US warship.
Japan's Coast Guard said none of the 20 crew members aboard the merchant vessel were injured. Such incidents are rare.
In May, the US Navy's USS Lake Champlain collided with a South Korean fishing vessel but both ships were able to operate under their own power.
The 7th Fleet commander, Vice Admiral Joseph Aucoin thanked the Japanese Coast guard in a post on the fleet's Facebook page, adding: "We are committed to ensuring the safe return of the ship to port in Yokosuka."