BEIJING, April 10 (Xinhua) -- China on Tuesday expressed serious concerns over a series of actions taken by Vietnam on Nansha Islands and their adjacent waters and lodged strong representations to the Vietnamese side.

    "China has indisputable sovereignty over the Nansha Islands and their adjacent waters and neighbouring marine areas," spokesman Qin Gang told a routine press conference.

    Qin made the remarks when asked to commented on Vietnam's plans to work with British Petroleum (BP) to build a gas pipeline on South China Sea and to hold local elections on the islands.

    According to reports, the pipeline, worth two billion U.S. dollars, will bring gas from two new fields to Vietnam's south coast and details are still being worked out.

    Any one-sided actions taken by any country in the waters are "illegal and invalid", constituting an encroachment upon the Chinese territorial sovereignty, sovereignty rights and administrative rights on the islands, said Qin.

    Qin said the situation on South China Sea is generally stable at present with efforts of parties concerned.

    "Vietnam's new actions, which infringe on China's sovereignty, sovereignty rights and administrative rights on the Nansha Islands, go against the important consensus reached by leaders of the two countries on the maritime issue and are not beneficial to stability of the South China Sea area," he added.