By J.R. Wu

KAOHSIUNG, Taiwan (Reuters) - Taiwan's coast guard on Saturday commissioned its biggest ships for duty in the form of two 3,000-ton patrol vessels, as the island boosts defenses amid concerns about China's growing footprint in the disputed South China Sea.

The new vessels will be able to dock at a new port being constructed on Taiping Island, the largest of the naturally occurring Spratly Islands in the South China Sea, before the end of this year.

Taiwan's coast guard has had direct oversight of the 46-ha (114-acre) island, also known as Itu Aba, since 2000.

"Taiping Island's defense capabilities will not be weak," said Wang Chung-yi, minister of the Coast Guard Administration, referring to recent upgrading done on the 1,200-metre (yards) long airstrip on Taiping and the building of a new port, which he said could be completed as early as October this year.

"As far as Taiping Island is concerned, we still maintain not so much a military as a civil role," Wang told Reuters in an interview in Taipei. Taiwan will not create conflict, but if it is provoked "we will not concede," he said.

Unlike the Philippines and Vietnam, Taiwan has largely avoided becoming ensnared in public disputes with China over the South China Sea, through which $5 trillion in ship-borne trade passes every year.

Beijing claims most of the South China Sea, while the Philippines, Brunei, Malaysia, Taiwan and Vietnam also have overlapping claims.

Rival claims by Taiwan and China go back to before defeated Nationalists fled to Taiwan after losing a civil war with the Communists in 1949.

Beijing sees self-ruled Taiwan as a renegade province to be retaken one day and bans actions that would confer sovereignty, such as negotiating territorial disputes in the South China Sea.

Taiwan President Ma Ying-jeou boarded one of the new ships on Saturday, observing rescue drills in waters off the southern Taiwan port city of Kaohsiung.

One of the vessels will be sent to the South China Sea, while the other will be assigned to waters north of Taiwan where it has overlapping claims with Japan.

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Japan's Yomiuri newspaper reported on Saturday that Group of Seven leaders meeting in Germany on Sunday would express their concern over any unilateral action to change the status quo in the East and South China Seas.

China has been criticized for extensive reclamation work and moves to turn submerged rocks into man-made structures. The United States last week said Beijing had placed mobile artillery systems in contested territory.

(Editing by Jeremy Laurence)