Beijing - China on Tuesday protested Vietnam's "illegal" appointment of a governor for the disputed Xisha islands in the South China Sea. "China has indisputable sovereignty over the Xisha islands and their adjacent waters," foreign ministry spokeswoman Jiang Yu said in a statement.

Vietnam's April 25 appointment of a chairman of a People's Committee for the islands - also known internationally as the Paracels, and in Vietnam as the Huyen dao Hoang Sa - was "illegal and invalid," Jiang said.

The Chinese government has informed Vietnam of its position on the appointment, she said.

The Xisha group includes more than 30 islets, sandbanks and reefs spread out in an area of about 15,000 square kilometres.

China last month said it planned to send more naval vessels to patrol the islands and other disputed areas of the South China Sea to counter illegal fishing and "other countries' unfounded territorial claims."

The official China Daily quoted a senior fisheries official as saying the government faced new "challenges and complications" in the South China Sea, pointing to recent claims by the Philippines and Malaysia to disputed islands and a standoff with a US naval surveillance ship.

In mid-March, China sent its largest and fastest fisheries ship, the Yuzheng 311, to patrol the Xisha group and nearby disputed islands.(dpa)