Dozens were injured when police used tear gas and rubber bullets to disperse the protesters, who fought back with umbrellas, bottles, bricks and poles, in areas near the liaison office.

Beijing resident Cissy Li said the scenes had changed her mind about the protests.

“In the past, I could share the Hong Kong people’s sentiment about political events and I very much supported them,” Li said. “But now I’m confused about these radicals – what are they really after?”

Observers said the escalating violence in Hong Kong could spur the leadership to take a more assertive stance in managing the city’s affairs in the future, weakening its autonomy.

Many across the border were deeply offended by images of the vandalised national emblem and obscenities levelled at mainland Chinese.

“[The protesters] have gone beyond the normal channels to express their opinions and became violent in order to press for their demands,” said a man surnamed Yue from Shijiazhuang in Hebei province.

His view was echoed by many social media users on Weibo, the Chinese version of Twitter.

The state broadcaster dedicated almost one-third of its strictly choreographed evening newscast to interviews and official statements criticising the protesters’ behaviour, and close-up images of the vandalised office building.

Media reports about the Yuen Long attacks could be found by mainlanders via posts on Weibo, but there was no mention in official media.

Tian Feilong, an associate professor at Beihang University’s law school, said the public mood could encourage Beijing to take a stronger line on Hong Kong.

“If the protests continue and push the Hong Kong government to its limit, and the government fails to respond to the current crisis, then Beijing will be forced to take some measures,” Tian said.

According to Tian, Beijing could take a more hardline position to try to end the situation if it deteriorates, with one option being to declare a state of emergency in Hong Kong and apply mainland laws in the city.

Police chief defends ‘late’ force response to mob violence in Yuen Long

He was referring to Article 18 under the Basic Law, the city’s mini-constitution. It states that the Standing Committee of the National People’s Congress can decide that Hong Kong is “in a state of emergency” on the grounds of turmoil that endangers national unity or security and is beyond the control of the Hong Kong government.

Under such circumstances, Beijing can “issue an order applying the relevant national laws” in Hong Kong.

Guo Wanda, executive vice-president of the China Development Institute, a think tank in Shenzhen, agreed. He said the protests in Hong Kong would prompt Beijing to take a tougher stance, especially if the violence continued.

But Zhu Jie, a professor specialising in Hong Kong law at Wuhan University, said the situation in the city was a long way off the stage where Beijing could justify such drastic action as declaring a state of emergency.

“Although the radical protesters are testing Beijing’s bottom line in terms of tolerance, we can see from the commentaries in state media that the central government is still restrained and continues to support the city’s government and the police,” Zhu said.

“Beijing will stick to the ‘one country, two systems’ principle and give Hong Kong a high degree of autonomy.”

Day after brutal attack on protesters, a Hong Kong ghost town

Qin Qianhong, another law professor from Wuhan University, agreed that declaring a state of emergency was a last resort and not a step that would be easily taken.

“Up until now, the protests have been generally peaceful and there’s no sign that the Hong Kong government and police have lost control,” Qin said.