TOKYO - Around 20 people were thrown into the sea, two of whom fell unconscious, after two boats used in a protest against the relocation of a US military base capsized off the coast of Henoko in Japan's island prefecture of Okinawa on Monday morning, local media reported.

The accident occurred shortly after 10:10 am local time in waters off Henoko in the city of Nago, where construction work is underway to relocate the US Marine Corps Air Station Futenma, public broadcaster NHK reported.

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The two vessels, carrying around 20 people protesting the relocation construction, overturned, causing those on board to fall into the water, the report said.

Two of the individuals were transported to a hospital in an unconscious state, while more than a dozen others sustained non-life-threatening injuries, it added.

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The coast guard and local fire departments are continuing search and rescue operations while investigating the details of the accident.