US destroyer collides with merchant vessel near Japan
The crash involving the USS Fitzgerald happened 56 nautical miles (103km) south-west of the city of Yokosuka at about 2:30am local time (18:30 BST) on Saturday.
Japan's public broadcaster, NHK, showed aerial footage of the US ship with heavy damage on one side.
The US Navy has requested help from the Japanese coastguard.
One injured sailor is to be evacuated to hospital by the coastguard's helicopter, the navy said.
A spokesperson also told Reuters news agency that the ship was working to account for all personnel.
In a series of tweets, the US 7th Fleet earlier said the USS Fitzgerald had experienced flooding in some areas, and the extent of injuries was being determined.
It said the ship was now on its way to Yokosuka - under its own power, but with limited propulsion.
It also said the other ship carried a Filipino flag.
In a statement released on social media, Admiral John Richardson said: "As more information is learnt we will be sure to share it with the Fitzgerald families and when appropriate the public. [...] All our thoughts and concerns are with the Fitzgerald crew and their families."
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