Beijing (CNN) The Chinese government has accused pro-democracy protesters in Hong Kong of committing "evil and criminal acts" that have seriously damaged the semi-autonomous city's "reputation" and "stability."

At a press conference in Beijing on Monday, Hong Kong and Macau Affairs Office spokesman Yang Guang called the situation in Hong Kong "grave," adding that Beijing would not allow any challenge to the Chinese government's authority or threats to national security.

"No civilization or society under the rule of law would ever allow acts of violence to take place. We call on the general public of Hong Kong to be aware of the grave nature of the current situation," Yang said, calling on Hong Kong citizens to condemn protester violence.

"Hong Kong is China's Hong Kong. Hong Kong's affairs are China's domestic affairs," he added. Hong Kong has been governed under a " one country, two systems " model since the city transferred from British to Chinese rule in 1997.

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It was the first time China's top Hong Kong policy office had given a briefing on the mass demonstrations that began in early June in opposition to a controversial -- and now-shelved -- bill that would have allowed extradition from the city to mainland China.