Japan's central government is set to start landfill work in the Henoko district on the coast of Okinawa as the next step to relocate a US military base within the prefecture.
The government plans to bring sand and soil onto the site for the reclamation on Friday. It says preparations have been made, including repair of seawalls damaged by a typhoon.
The Defense Ministry's regional bureau in Okinawa will load the landfill from a vessel to dump trucks which will drive to the site, about 2 kilometers away. The work is expected to begin as early as before noon.
On Friday morning, about 50 protesters gathered outside US Camp Schwab near the planned reclamation site.
They put up placards demanding the suspension of the work, calling it illegal. Skirmishes broke out between the protesters and riot police.
The Okinawa prefectural government is calling on the central government to suspend the work, saying it is against the will of local people.
On Thursday, Okinawa Governor Denny Tamaki again conveyed his opposition when he met Chief Cabinet Secretary Yoshihide Suga and Defense Minister Takeshi Iwaya.
But the central government said it will proceed with the work of relocating the US Futenma air base in Ginowan City to the less populated coastal area to remove the dangers posed by the base in its current site.
The relocation work is expected to enter a new stage since the plan was first discussed between the US and Japanese governments more than 20 years ago.