An attack on the office of Beijing's representative in Hong Kong by protesters was a "blatant challenge to the central government" and will not be tolerated, state news agency Xinhua says in an editorial.
Thousands of protesters gathered outside China's Liaison Office on Sunday, throwing eggs and spray-painting graffiti on its walls. Riot police used tear gas and rubber bullets to drive them away.
"When the majestic national emblem of the People's Republic of China was defaced with black paint, it caused unbearable pain and anger," Xinhua said on Monday.
"These illegal acts are unacceptable to all Chinese people, including the people of Hong Kong."
"The escalating violence and provocative acts have completely exposed these mobs and the forces behind them," it said.
The unrest in Hong Kong was triggered by attempts to introduce amendments to the city's extradition law that opponents said would allow Beijing to try democracy activists in mainland courts.
China has consistently blamed the violence on "lawlessness" and "foreign interference".
The English-language China Daily said in another editorial on Monday business leaders and other organisations had "had enough of the radical youths" and were demanding an end to the violence.
Australian Associated Press