TOKYO -- Japan's coast guard is investigating why it took nearly an hour for a deadly collision between a U.S. Navy destroyer and a container ship to be reported.

A coast guard official said Monday they are trying to find out what the crew of the Philippine-flagged ACX Crystal was doing before reporting the collision off Japan's coast to authorities 50 minutes later.

The ACX Crystal collided with the USS Fitzgerald off Japan's coast, killing seven of the destroyer's crew of nearly 300. The ships collided early Saturday morning, when the Navy said most of the 300 sailors on board would have been sleeping. Authorities have declined to speculate on a cause while the crash remains under investigation.

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A track of the much-larger container ship's route by MarineTraffic, a vessel-tracking service, shows it made a sudden turn as if trying to avoid something at about 1:30 a.m., before continuing eastward. It then made a U-turn and returned around 2:30 a.m. to the area near the collision.

The impact crushed the starboard side of the Fitzgerald. The ship was listing as it sailed into its home port in Yokosuka, Japan, Saturday, CBS News correspondent Ben Tracy reports. The commander of the U.S. 7th Fleet said the sailors' actions kept the ship from sinking.

"This was not a small collision," Vice Adm. Joseph Aucoin said. "It was right near the pilot's house, and there is a big puncture."

This combination of undated photos released June 19, 2017, by the U.S. Navy shows the seven U.S. sailors who died in a collision between the USS Fitzgerald and a container ship off Japan on June 17, 2017. From top left to right, Personnel Specialist 1st Class Xavier Alec Martin, 24, from Halethorpe, Maryland; Yeoman 3rd Class Shingo Alexander Douglass, 25, from San Diego, California; Gunner's Mate Seaman Dakota Kyle Rigsby, 19, from Palmyra, Virginia; and Fire Controlman 2nd Class Carlos Victor Ganzon Sibayan, 23, from Chula Vista, California. From bottom left to right, Sonar Technician 3rd Class Ngoc T Truong Huynh, 25, from Oakville, Connecticut; Gunner's Mate 2nd Class Noe Hernandez, 26, from Weslaco, Texas; and Fire Controlman 1st Class Gary Leo Rehm Jr., 37, from Elyria, Ohio. U.S. Navy via AP

The Crystal sustained minor damage to its bow. The cargo ship, which is about four times heavier, nearly T-boned the Navy destroyer when much of the crew was asleep and the bridge likely manned by less than a dozen people, Tracy reports.

The coast guard initially said the collision occurred at 2:20 a.m. because the Philippine ship had reported it at 2:25 a.m. and said it just happened. After interviewing Filipino crewmembers, the coast guard has changed the collision time to 1:30 a.m.

Coast guard official Tetsuya Tanaka said they are trying to resolve what happened during the 50 minutes.

He said officials are planning to get hold of a device with communication records to examine further details of the crash. Japan's Transport Safety Board also started an accident investigation on Sunday.

Adding to the confusion, a U.S. Navy official said it is sticking with the 2:20 a.m. timing for the crash that he said had been reported by the Fitzgerald.

Asked about the earlier time cited by the coast guard, Navy spokesman Cmdr. Ron Flanders said, "That is not our understanding." He said any differences would have to be clarified in the investigation.

Nanami Meguro, a spokeswoman for NYK Line, the ship's operator, agreed with the earlier timing.

Meguro said the ship was "operating as usual" until the collision at 1:30 a.m., as shown on a ship tracking service that the company uses. She said the ship reported to the coast guard at 2:25 a.m., but she could not provide details about what the ship was doing for nearly an hour.

"Because it was in an emergency, the crewmembers may not have been able to place a call," she said.

Coast guard officials are investigating the case as possible professional negligence, but no criminal charges have been pressed so far.

On Monday, the 7th Fleet identified the seven sailors who died. Navy divers recovered the bodies after the severely damaged Fitzgerald returned to the fleet's home in Yokosuka, Japan, with assistance from tug boats.

The victims were Gunner's Mate Seaman Dakota Kyle Rigsby, 19, from Palmyra, Virginia; Yeoman 3rd Class Shingo Alexander Douglass, 25, from San Diego, California; Sonar Technician 3rd Class Ngoc T Truong Huynh, 25, from Oakville, Connecticut; Gunner's Mate 2nd Class Noe Hernandez, 26, from Weslaco, Texas; Fire Controlman 2nd Class Carlos Victor Ganzon Sibayan, 23, from Chula Vista, California; Personnel Specialist 1st Class Xavier Alec Martin, 24, from Halethorpe, Maryland; and Fire Controlman 1st Class Gary Leo Rehm Jr., 37, from Elyria, Ohio.

White House press secretary Sean Spicer said President Trump and the entire administration was sending their thoughts and prayers to the sailors' families.

Spicer said the incident was a "sobering reminder of the dangers" faced by the men and women of the U.S. military every day.

In a statement, acting Navy Secretary Sean Stackley said, "We are all deeply saddened by the tragic loss of our fellow shipmates. ... As details emerge, we can all be proud of the heroic effort by the crew to tend to the needs of those injured and save the ship from further damage while returning safely to port."

He thanked "our Japanese allies" for their swift assistance, and said the Navy will fully investigate the cause.

Connecticut Gov. Dannel Malloy ordered flags flown at half-staff there in memory of Huynh.

Huynh's sister, Lan Huynh, told WVIT-TV that the family is coping as best they can.

She described her brother as "selfless" and said he always "had the brightest smile."

The mother of another sailor on the ship said her son kept diving in his flooded berth after the crash to try to save his shipmates until it began running out of air pockets, while other survivors - believing their ship was under attack - hurried to man the guns.

Mia Sykes of Raleigh, North Carolina, told The Associated Press on Sunday that her 19-year-old son, Brayden Harden, was knocked out of his bunk by the impact and water immediately began filling the berth.

Sykes said her son told her that four men in his berth died, including those sleeping on bunks above and below him, while three died in the berth above his.

She said she hopes her son, from Herrin, Illinois, can come home to be with family as he works through what happened. "You have to realize most of them are 18-, 19- and 20-year-olds living with guilt. But I told him, 'There's a reason you're still here and make that count.'"