China's Kunming airport has shut down on Saturday as heavy fog kept shrouding the major air hub in southwest China since Friday night, the airport's administration announced. Neither of the airport's two runways is suitable for taking off nor landing. According to the airport's administration, poor visibility led to the cancellation of 13 flights by so far, and 310 flights are waiting to take off from the airport on Saturday. The visibility is expected to improve around noon.