China had informed Vietnam of its test flights on Yongshu Jiao, one of the Nansha Islands on which China has built an airport, said Foreign Ministry spokesman Hong Lei on Thursday.

The Flight Inspection Center of the Civil Aviation Administration of China informed the Ho Chi Minh Flight Information Region at 17:46 on Dec 28 of the flight plan, route and other technical information of China's inspection aircraft, "before China had to turn the flights into state aviation activities due to Vietnam's groundless obstruction," he said.

This is the second time in four days the Foreign Ministry responded to Vietnam's claims of having not received notification of the test flights.

"We are shocked and bewildered by the repeated arguments by Vietnam," Hong said, adding that China's test flights from the airport of Yongshu Jiao is in accordance to international law and international conventions.

"China has indisputable sovereignty over the Nansha Islands and their adjacent waters," he reiterated.

On Jan 2, Foreign Ministry spokeswoman Hua Chunying confirmed that China had conducted a test flight on the newly built airport on Yongshu Jiao that drew objections from Vietnam, which also claims sovereignty over the island.

On Jan 6, China conducted another test flight with two civil planes.