(VOVWORLD)- Vietnam's northern mountainous region is experiencing the coldest spell since the beginning of winter. According to the National Center for Hydro-meteorological Forecasting, this is one of the six cold spells with the lowest temperatures in the past 40 years. At Mau Son mountain peak in Lang Son province, about 1,500 meters high above the sea level, the temperature drops to minus defrees Celsius with first frost seen from 3 am on Sunday.