Fireworks exploded over Victoria Harbour to mark 20 years of Chinese rule, but President Xi Jinping, who travelled to Hong Kong for the occasion, had some harsh words. He warned that Beijing would not tolerate any challenge to its authority. “Any attempt to endanger China’s sovereignty and security, challenge the power of the central government ... or use Hong Kong to carry out inltration and sabotage activities against the mainland is an act that crosses the red line and is absolutely impermissible,” Mr. Xi said.

Soon after he left the island, protesters took out annual pro-democracy marches, some carrying a large image of jailed Chinese Nobel Peace laureate Liu Xiaobo. Hong Kong was handed over by the British to China two decades ago in a tearful farewell. The Chinese President and Hong Kong Chief Executive Carrie Lam watched a presentation during their visit to a section of the Hong Kong-Zhuhai-Macau Bridge, which is under construction. This was Mr. Xi’s first visit to Hong Kong after he became President in 2013.