A police officer stands guard in front of barricades near the Hong Kong Convention and Exhibition Center ahead of a three-day visit by the National People's Congress Chairman Zhang Dejiang in the Wan Chai district of Hong Kong, China, on Monday, May 16, 2016. Hong Kong was on its highest security alert Tuesday -- with about a fifth of the city's police force mobilised -- as one of China's top leaders arrive amid political tensions over Beijing's rule of the former British colony. Photographer: Justin Chin/Bloomberg via Getty Images
