SWAT policemen take part in an anti-riot exercise in a rail yard of the Yinchuan department of Lanzhou Railway Bureau in Yinchuan, capital of northwest China's Ningxia Hui Autonomous Region, Jan. 12, 2017. The exercise was held to improve security capacity for the upcoming Spring Festival travel rush. (Xinhua/Peng Zhaozhi)

SWAT policemen take part in an anti-riot exercise in a rail yard of the Yinchuan department of Lanzhou Railway Bureau in Yinchuan, capital of northwest China's Ningxia Hui Autonomous Region, Jan. 12, 2017. The exercise was held to improve security capacity for the upcoming Spring Festival travel rush. (Xinhua/Peng Zhaozhi) 

SWAT policemen take part in an anti-riot exercise in a rail yard of the Yinchuan department of Lanzhou Railway Bureau in Yinchuan, capital of northwest China's Ningxia Hui Autonomous Region, Jan. 12, 2017. The exercise was held to improve security capacity for the upcoming Spring Festival travel rush. (Xinhua/Peng Zhaozhi)

SWAT policemen take part in an anti-riot exercise in a rail yard of the Yinchuan department of Lanzhou Railway Bureau in Yinchuan, capital of northwest China's Ningxia Hui Autonomous Region, Jan. 12, 2017. The exercise was held to improve security capacity for the upcoming Spring Festival travel rush. (Xinhua/Peng Zhaozhi)