"The Central government will continue to firmly and unshakably support legal measures and policies taken by administration leader CY Leung and the police of the special territory in handling these illegal protests according to the law," a front-page editorial said.
The piece in the Communist Party mouthpiece People's Daily also warned that "if matters are not dealt (with) according to the law, Hong Kong society will fall into chaos".
It described the protesters -- who are calling for unrestricted democracy and for Leung to resign -- as "selfishly" disrupting social order in a way that "harms social stability and economic prosperity of Hong Kong".
Since the street protests escalated on Sunday, Beijing has given its full backing to the city's authorities and voiced opposition to what it terms "illegal acts".
On Wednesday in Washington, Foreign Minister Wang Yi warned against outside interference, saying "Hong Kong affairs are China's internal affairs".
Beijing has heavily censored all information in mainland China related to the Hong Kong protests, which have brought thousands of people onto the streets.
This week authorities detained more than a dozen activists across China and questioned as many as 60 others who have expressed support for Hong Kong's pro-democracy movement, according to the advocacy groups China Human Rights Defenders and Amnesty International.
"The rounding up of activists in mainland China only underlines why so many people in Hong Kong fear the growing control Beijing has in their city's affairs," Amnesty's China researcher William Nee said in a statement in response to the clampdown.