South Korean activists gathered Saturday on a southern holiday island to protest against the construction of a navy base, a day after hundreds of riot police dispersed demonstrators blocking the work.

About 300 activists and opposition party members flew to Jeju island to join protesters already there, Yonhap news agency reported.

They plan a "peace event" including a concert and cultural activities to demonstrate opposition to the planned base at Gangjeong village on the south coast.

Protesters say the base, which will be open to US forces, will damage the environment and could spark disputes with China over the American presence.

Opponents have occupied the site since June, preventing construction.

Police dispersed about 130 people on Friday and arrested 38 of them. Scuffles broke out but no serious violence was reported.

Construction workers later Friday completed a fence around the site.

Jeju police have sent 230 officers to support 606 riot police already stationed in Gangjeong, some of them dispatched from the mainland.

Military officials say the $970 million project is vital for national security. Once completed in 2014 it will host some 20 warships, including submarines, to help protect shipping lanes through which virtually all the country's sea trade passes.

The deployment will also help guard against sea infiltration by North Korea and could quickly respond to territorial disputes with neighbouring states, the military has said.

Some islanders support the project for the boost it will give the local economy.

Opponents ranging from environmentalists to religious leaders and anti-government activists allege South Korea bowed to pressure from the United States, which they say is eager to establish a military presence near China.

Both Seoul and Washington, which stations 28,500 troops in South Korea, deny the accusation.