The US Navy's top commander visited Japan Tuesday to meet the grieving families of seven sailors killed in a weekend accident, as investigators probe questions over the timing of the collision with a container ship.

Admiral John Richardson arrived at the US naval base in Yokosuka on the outskirts of Tokyo to meet bereaved relatives and officers who served on the USS Fitzgerald.

"It's an intimate meeting, very solemn grieving with families, so we're not even taking photos," Commander Ron Flanders, press officer at the US Naval Forces in Japan, told AFP.

The sailors, aged 19 to 37, were found in flooded sleeping berths a day after the collision tore a huge gash in the side of their guided-missile destroyer.

Their bodies were being flown back to the US on Tuesday morning, according to the Commander US Naval Forces Japan.

"Fitzgerald 7 are headed home; just left Japan... crew, family on hand to say goodbye," it said on Twitter.

Japanese coastguard investigators have been interviewing the Filipino crew of the cargo ship ACX Crystal, and hope to directly hear accounts of sailors aboard the much-smaller US destroyer.

The cargo ship's crew -- who were not injured -- apparently took nearly an hour to report the collision in a busy shipping channel near the warship's home base, a gateway to container ports in Tokyo and nearby Yokohama.

Originally, Japan's coastguard said the crash happened at 2:20 am Saturday (1720 GMT Friday) based on when it was reported by the Crystal's crew.

But they later told Japanese investigators the incident actually happened almost an hour earlier at 1:30 am.

Japanese officials are also investigating why the 222-metre (730-foot) cargo ship made a sudden turn at about 1.30 am, and a sharp turn after it reported the accident around 2:20 am, as shown in data from the Marine Traffic website.

It was not clear why the crew waited almost an hour to report the collision or what prompted the turns.

"As to the chronological order of what happened and other details, we are still investigating," a Japanese coastguard spokesman said.

The US destroyer did not report the accident to local authorities and was not obliged to, he added.

The United States has primary jurisdiction in investigating accidents involving its military.

There have been around 30 ship collisions over the past decade in the area, including a 2013 incident in which six Japanese crew died.

Richardson would also meet Japanese Maritime Self-Defence Force and coastguard officials to express his appreciation for their help in the search, Kyodo News reported.

Source: AFP