The US Navy said a number of missing sailors were found dead in damaged areas of a destroyer that collided with a container ship off Japan's coast, with Japanese public broadcaster NHK saying all seven crew had died.

"The sailors were located by divers, deceased. Taken to USNH Yokosuka for ID," the Commander of US Naval Forces in Japan said on Twitter. In a separate statement that did not confirm the deaths, the US 7th Fleet said a "number" of crew had been found.

"As search and rescue crews gained access to the spaces that were damaged during the collision this morning, the missing Sailors were located in the flooded berthing compartments," it added.

"They are currently being transferred to Naval Hospital Yokosuka where they will be identified."