Coast guard official Tetsuya Tanaka said they are trying to resolve what happened during the 50 minutes. Two crew members, including the destroyer's commanding officer, were medically evacuated.
Aucoin said the final toll was not being released "out of respect for their families". "I am humbled by the bravery and tenacity of the Fitzgerald crew".
Most of the almost 300 sailors aboard would have been asleep in their berths at the time of the collision.
Fire Controlman 1st Class Gary Leo Rehm Jr. was among seven sailors killed aboard the USS Fitzgerald on Saturday.
He also praised their colleagues for saving the USS Fitzgerald from further damage and taking it back to port.
A Navy spokesman said the victims might have been killed by the impact of the collision or drowned in the flooding.More news: Ward demands pound-for-pound recognition after Kovalev stoppage
Four hundred ships a day sail through this gulf toward Japan's biggest port, and the traffic, the scattering of islands, and the lights on land can make navigation extremely hard. "The Navy owes the family and the nation a prompt investigation", Blumenthal said.
He was evacuated by helicopter and was in a stable condition at a U.S. navy hospital in Yokosuka, where the Seventh Fleet is based, the navy said. U.S. Navy personnel set up support and counseling services to help families as they sought updates on crew members.
"We are fully cooperating with the investigation", said Manami Meguro, a spokeswoman for Nippon Yusen.
A "tremendous" amount of water flooded through the huge gash, in the words of Vice Adm. Joseph Aucoin, commander of the US 7th Fleet.
Crew members of the Philippine ACX Crystal container vessel have been questioned on suspicion of possible endangerment of traffic caused by professional negligence. "The damage is mostly underneath the water line, and it's a large gash near the keel of the ship". "I can promise you it will be very thorough and there will be people held to account for this".More news: Bihar governor Ram Nath Kovind is BJP's presidential nominee
U.S. Navy Chief of Naval Operations Adm. John Richardson said four sailors were medevaced.
Several U.S. Navy aircraft, as well as Japanese Coast Guard and Japan Maritime Self-Defense Force helicopters, ships and aircraft were deployed to render assistance to the Fitzgerald, a release said. "He's okay. Thank you all for the prayers", Rita Schrimsher of Athens, Alabama, tweeted after speaking with her 23-year-old grandson, Jackson Schrimsher, via Facetime.
The container ship ACX Crystal weighs 29,060 tons and is 730 feet long, much larger than the 8,315-ton Navy destroyer.
The navy's acting secretary Sean Stackley said "we are all deeply saddened by the tragic loss of our fellow shipmates".
The Fitzgerald was returning to a USA naval base in Japan after completing a training exercise with US and Japanese warships.
But when the sun came up and photos appeared of both ships, they revealed the Crystal had damage on the left or port side of its bow - suggesting it might have been traveling in the same direction as the Fitzgerald.More news: North Korea test-fires four anti-ship missiles
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