Two US sailors were treated for minor injuries from the fire which broke out on the USS New Orleans in the southern island of Okinawa on Wednesday, the US 7th Fleet said in a statement.

"The cause of the fire is currently under investigation... New Orleans' crew will remain aboard the ship," the statement said.

The 208.4-metre (684-foot), 24,433-ton amphibious transport dock ship is anchored off the White Beach Naval Facility.

Japan's Coast Guard said that initially the US military sought assistance from Japan, but then cancelled the request before then renewing it around 7:30 pm (1030 GMT).

Four Japanese vessels -- from the Coast Guard, the navy and private contractors -- spent the night dousing the blaze, spokesman Tetsuhiro Azumahiga told AFP.

The United States has around 54,000 military personnel stationed in Japan, mostly on Okinawa.