Frost blanketed several mountains in northern Vietnam as temperatures fell below zero degrees Celsius on Monday and Tuesday. A frost-covered tree on Phja Oac Mountain. The frost enveloped tree branches from an altitude of about 1,000 meters up to the mountain’s summit, at 1,520 meters. Frost forms on Phja Oac Mountain in Cao Bang Province as the temperature falls to minus two degrees Celsius. The cold spell will last until Thursday and has resulted in temperatures of 7-10 degrees Celsius in the region and below zero degrees Celsius in high mountain areas, according to the National Center for Hydro-Meteorological Forecasting.