Government workers on Monday resumed offshore work off the coast of Nago, Okinawa Prefecture, to build the replacement facility for U.S. Marine Corps Air Station Futenma as protesters gathered to halt the project.

Some 100 protesters started gathering at dawn in front of the gate of Camp Schwab next to a site for reclamation work to block construction vehicles from entering.

At around 9:30 a.m., riot police tried to remove protesters sitting in front of the gate with their arms crossed.

The protesters shouted, “Stop violence!” and “Don’t hurt the Okinawans!”

“I saw vessels coming on TV, and I couldn’t just sit around doing nothing,” said a 70-year-old man from Urasoe. “Okinawa can’t stay like a colony of Japan and the U.S.”

The work began after U.S. Defense Secretary James Mattis and Prime Minister Shinzo Abe agreed last week to go ahead with the base relocation.

The work is part of the central government’s plan to relocate U.S. Marine Corps Air Station Futenma from densely populated Ginowan to the Henoko coastal area in Nago. Both are on the main island of Okinawa.

Okinawa Gov. Takeshi Onaga returned from Washington on Sunday evening after relaying local opposition to the plan to the administration of President Donald Trump.

He is likely to try thwarting the project refusing to give permission for moving coral reefs in the planned reclamation area and by taking other steps.

“Based on relevant law, the government will pay as much consideration as possible to the natural environment and the livelihoods of the local people as we move forward with work to relocate (the base to) Henoko,” Chief Cabinet Secretary Yoshide Suga said.

Tokyo has argued that the base relocation accord with Washington is “the only solution” for eliminating the dangers posed by the Futenma base without undermining the deterrence provided by the Japan-U.S. security alliance.

The Okinawa Prefectural Government, however, is seeking to boot base out of the prefecture altogether.

The offshore work will place more than 200 concrete blocks to act as a screen to prevent debris and sediment generated from coastal revetment work from spreading. The central government will also conduct an undersea survey.

Ahead of the construction work, a group of vessels carrying concrete blocks arrived near the site Sunday. The ships will also be used to carry out the survey.

After starting relocation work in Henoko in October 2015, the central government suspended it in March last year following an agreement with Okinawa under court mediation as part of efforts to break the impasse on the issue.

But Tokyo resumed land construction work on Dec. 27 at the U.S. Marines’ Camp Schwab neighboring the relocation site after the Supreme Court ruled against Okinawa’s opposition in a case brought by the central government in July.