Constructors work inside the Guantian Tunnel of the Zhangjiajie-Jishou-Huaihua high speed railway, central China's Hunan Province, Dec. 3, 2018. The 246.6 km-long high speed railway will pass through Zhangjiajie City, Tujia-Miao Autonomous Prefecture of Xiangxi and Huaihua City with a designed speed of 350 km per hour. (Xinhua/Xing Guangli)