The first bullet train of the Harbin-Mudanjiang high-speed rail line leaves Harbin Railway Station in Harbin, northeast China's Heilongjiang Province, Dec. 25, 2018. A high-speed railway line officially went into operation on Tuesday, linking cities of Harbin and Mudanjiang in China's northernmost province of Heilongjiang, where the temperatures dip as low as minus 40 degrees Celsius. (Xinhua/Wang Jianwei)