WASHINGTON (REUTERS, AFP) - Seven crew members are missing and at least three injured after a US Navy destroyer collided early on Saturday (June 17) morning with a Philippine-flagged merchant vessel south of Tokyo Bay in Japan, the US Navy said.

US Navy destroyer USS Fitzgerald, which was experiencing some flooding, managed to sail back to its base in Yokosuka, while the merchant vessel appeared to have relatively minor frontal damage.

The US Navy said in a statement the USS Fitzgerald collided with container ship ACX Crystal at about 2.30am local time (1.30am Singapore time), some 56 nautical miles south-west of Yokosuka, a rare incident on a busy waterway. At 222-metres and around 29,000 tonnes displacement, the merchant vessel is about three times the size of the US warship.

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.

Benson took command of the Fitzgerald on May 13. He had previously commanded a minesweeper based in Sasebo in western Japan.

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 had 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".

'MERCHANT VESSEL MADE SHARP TURN'

The area is a busy shipping channel that is a gateway to major container ports in Yokohama and Tokyo.

"The volume of ships is heavy in this area and there have been accidents before," coastguard official Yutaka Saito told Japan's public broadcaster NHK.

NHK said the massive 222m container ship made a sharp turn around the time of the accident, but its captain suggested otherwise. "(We) were sailing in the same direction as the US destroyer was and then collided," he was quoted as saying by Jiji Press news agency.

Japan's Coast Guard, which is probing the incident, said it has sent a half dozen vessels, several aircraft and a team of specially-trained rescue personnel to the scene. They were later joined by the country's Self-Defence Forces.

"We're going all out in the search to find these missing people... but we still haven't found any clues about where they might be," a coastguard spokesman said, adding that the search may continue overnight.

A spokesman for the US 7th Fleet said: "Once an investigation is complete then any legal issues can be addressed."

None of the 20 crew on ACX Crystal were injured, the Coast Guard said.

ACX Crystal, which was on its way to Tokyo, is chartered by Japan's Nippon Yusen KK. The company said in a statement it would "cooperate fully" with the Coast Guard's investigation of the incident.

The USS Dewey and two Navy tugboats were being 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.

Part of an eight-ship squadron based in Yokosuka, the Fitzgerald had in February completed US$21 million (S$29 million) worth of upgrades and repairs.

"My daughter is on the Fitzgerald," a parent wrote on the 7th Fleet's Facebook page. "So worried. Just need to hear she is ok. Thinking of all of our sailors and their families!!"

US chief of naval operations Admiral John Richardson said in a statement: "As more information is learned we will be sure to share it with the Fitzgerald families and when appropriate the public.

"All of our thoughts and concerns are with the Fitzgerald crew and their families."

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.