The Civil Aviation Authority of Vietnam (CAAV) has informed the International Civil Aviation Organization (ICAO) of the appearance of some unidentified aircraft in the flight information region of Ho Chi Minh City between January 1 and 6.
CAAV said in a report sent to ICAO that the aircraft did not make contact with Vietnamese air traffic authorities, news website VnExpress reported.
Lai Xuan Thanh, CAAV’s chief, said these were the first airspace violations in several years.
He said they were serious and may affect aviation activities in the region.
The flight information region of Ho Chi Minh City is colored blue.
Thanh added that Vietnamese flight management authorities had not received any announcements from China regarding its pilot flight to an airport built illegally on a reef in Truong Sa (Spratly) Islands in the East Sea.
On January 2, a civilian aircraft used by the Chinese government conducted a test flight at the new airport on Da Chu Thap (Fiery Cross Reef) in the Spratly Islands.
Vietnam's foreign ministry then sent a diplomatic note to Chinese embassy in Hanoi opposing China’s action.
But on January 6, Chinese media reported that the Chinese government would continue to conduct two more flights to the Fiery Cross airport. Vietnam later issued another rebuke to Beijing, saying its northern neighbour of "threatening peace."