HONG KONG (AP) — Chinese President Xi Jinping landed in Hong Kong Thursday to mark the 20th anniversary of Beijing taking control of the former British colony, accompanied by a formidable layer of security as authorities showed little patience for pro-democracy protests.

After stepping off his Air China plane, Xi said he envisioned "stable development" of Hong Kong's "one country, two systems" framework. Pro-democracy activists fear Beijing is undermining the principle — agreed upon when Britain handed over the city back to China — which guarantees Hong Kong can mostly run its own affairs and keep civil liberties including free speech until 2047.

Xi's three-day visit culminates Saturday when he will oversee an inauguration ceremony for the Asian financial hub's new leader, Carrie Lam.

Pro-democracy activists staged protests ahead of his visit and more were expected, including an annual march through the streets on Saturday that has drawn big crowds in the past. Hong Kong authorities were taking no chances with disruptions and deployed heavy security across the city.

Helicopters hovered overhead and police and barricades lined the streets around a downtown convention center and hotel complex where Xi was expected to spend most of his time. Officers questioned passers-by taking photos of the few protests allowed near the area. Authorities even glued the gaps between sidewalk paving stones in an effort to prevent them from being torn up and thrown by protesters.

Three pro-democracy groups said 26 of their members were arrested Wednesday evening on public nuisance charges for staging a sit-in at a giant flower sculpture near the complex. They were still detained hours after Xi arrived. Police have the power to hold them up to 48 hours.

Those arrested included Joshua Wong, the young activist who helped lead 2014's "Umbrella Movement" protests, and Nathan Law, another student protest leader who was elected to the legislature last year.

Xi is visiting to mark the 20th anniversary of Hong Kong's handover, when Britain ceded control of its colony to China at the stroke of midnight on June 30, 1997.

"It's been nine years since I last set foot in this place. I'm thrilled," Xi said on the airport tarmac. "Hong Kong has been tugging away at my heart," he said, adding that the anniversary of Hong Kong's "return to the motherland" on Saturday is "a big deal, a joyous occasion for the country and for Hong Kong."

He said one of the purposes of his trip is to plan for Hong Kong's future.

"We would like to look back at Hong Kong's extraordinary journey over the past 20 years, to learn from our experience, and look forward to the future to ensure the stable development of 'one country, two systems,'" he said in brief remarks before speeding off in a motorcade without answering questions.

Hong Kongers have grown concerned Beijing is backtracking on "one country, two systems" following a string of recent incidents, most notably the secret detention of five Hong Kong booksellers on the mainland.

Xi later visited the site of an arts hub under construction in West Kowloon district and was due to attend a banquet with government officials.

On Friday, he's expected to inspect Chinese troops at a People's Liberation Army base. China's only aircraft carrier, the Liaoning, will pay its first Hong Kong port call to mark the PLA's 20 year-presence in the city, the Defense Ministry said.

The ship, commissioned in 2012, and its battle group departed northern China on a training mission earlier this week and will likely pass through the Taiwan Strait along its voyage to Hong Kong.

Speaking at a monthly news briefing, ministry spokesman Col. Wu Qian said the ship would take part in "celebratory activities," but gave no details. Media reports said the ship would arrive in Hong Kong on July 7 for a two-day visit.

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Associated Press writer Christopher Bodeen in Beijing contributed to this report.