On the 20th anniversary of Hong Kong's return to China after more than 150 years of British rule, Chinese leader Xi Jinping has warned residents of the territory not to cross a "red line" by challenging Beijing's authority.

It was the first visit by Xi to Hong Kong since he became the leader of China in 2013. He spoke at a swearing-in ceremony for Carrie Lam, who becomes the new "chief executive" of the territory.

"Any attempt to endanger China's sovereignty and security, challenge the power of the central government... or use Hong Kong to carry out infiltration and sabotage activities against the mainland is an act that crosses the red line and is absolutely impermissible," Xi was quoted by The South China Morning Post as saying.

July 1 marks the anniversary of the 1997 handover of Hong Kong by Britain. Each year on the date, pro-democracy activists hold a demonstration to protest what they see as Beijing's crackdown on civil liberties in the territory. This year, activists were disappointed by a turnout they said amounted to only about 60,000 people. Hong Kong police put the figure at under 15,000.

Lam, who had been the No. 2 government official in the territory, took a hardline toward student-led pro-democracy protests in 2014.

Xi's speech on Saturday follows remarks critical of Beijing's administration of Hong Kong made by Chris Patten, the last British governor in the territory. As we reported Friday, Patten, in an editorial published in The New York Times, had harsh words for China's attacks on Hong Kong's independent judiciary and rule of law.

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