Workers began placing buoys off Okinawa as part of a long-planned and highly contentious relocation of an American military base, which a US official said was a critical step toward the realignment of US forces in Japan.
Japan and the United States have agreed on a plan that will see some land occupied by the US military returned to the islands, reports said.
The move is part of a broader arrangement designed to tamp down tensions in the US-Japan defence alliance.
The United States and Japan are hoping to break a stalemate over the US military presence on Okinawa.
The United States and Japan have agreed to tweak a six-year-old agreement on Marines based on the southern island of Okinawa.
Day in Pics: 20th September
Showbiz World - September 20, 2014
iPhone6 fever grips the world