Liu Xiaoming's warning at a news conference in London came as Chinese paramilitary forces conducted exercises across the border from Hong Kong.
Liu said if the situation continues to deteriorate in the region, the Chinese government would act to “quell unrest.”
“We have enough solutions and enough power within the limits of basic law to quell any unrest swiftly,” he said, referring to Hong Kong’s mini-constitution adopted after the former British colony was handed over to China in 1997. “Their moves are severe and violent offenses, and already shows signs of terrorism.”
He added: “The central government of China will never allow a few violent offenders to drag Hong Kong down a dangerous road, down a dangerous abyss.”
Meanwhile, hundreds of members of the People’s Armed Police were photographed at a Shenzhen soccer stadium where parking lots were filled with more than 100 dark-painted paramilitary vehicles, raising concerns that China might intervene to end 10 weeks of unrest across the harbor, Reuters reported.
"I don't know why they're here, but it could be related to Hong Kong," a ticket vendor at the stadium told Agence France-Presse, a Paris-based news wire service.
Inside the stadium, soldiers were seen conducting drills.
The stadium is just across a bridge that is one of the main access roads between the mainland and Hong Kong.
Chinese state media disputed claims that the government moved the vehicles in response to the protest, saying that exercises had been planned beforehand and were not directly related to the unrest in Hong Kong.
Protests that began in early June have paralyzed parts of the territory, including its international airport, and led to hundreds of arrests.
Flights have mostly resumed after being halted by mass demonstrations and spasms of violence on Monday and Tuesday. Police made five arrests Tuesday night and 17 more on Wednesday during clashes outside police stations in the Sham Shui Po district.
Protesters displayed laser pointers and burned spirit paper in recognition of the lunar calendar's traditional Hungry Ghost Festival, but police spokesman Tse Chun-chung said some also used catapults to fire metal balls and marbles at police. Officers responded with tear gas and "minimal use of force," he said.
Police were also maintaining airport checkpoints and restricting access to the facilities to those with travel documents, Tse said at a daily news briefing. While acknowledging some complaints about the use of tear gas and other aggressive police tactics in residential areas, Tse said police never wish to take such measures, and do so only when "appropriate."
"We hope everybody will join us in restoring and order in society," Tse said.
This week's clashes highlighted the hardening positions of pro-democracy protesters and the authorities, which show no sign of abating as long as the government continues to refuse calls for dialogue. Along with scrapping the extradition legislation, under which criminal suspects could be tried in mainland China and, critics say, face torture and unfair justice, protesters are demanding an investigation into alleged police abuses and other steps, with some calling also for the resignation of Chief Executive Carrie Lam.
The U.S. State Department said it was deeply concerned over reports that Chinese police forces were gathering near the border with Hong Kong and urged the city’s government to respect freedom of speech.
The department also issued a travel advisory urging U.S. citizens to exercise caution when visiting Hong Kong.
A total of 29 countries have issued travel safety alerts for Hong Kong, while international credit rating agencies have also expressed concern about the situation in the territory, city Financial Secretary Paul Chan said.
On Wednesday, President Trump suggested a “personal meeting” with Chinese President Xi Jinping to help “quickly and humanely solve the Hong Kong problem.”
“I have ZERO doubt that if President Xi wants to quickly and humanely solve the Hong Kong problem, he can do it. Personal meeting?” he tweeted.
More than 700 protesters have been arrested since the demonstrations began in the territory of 7.5 million in early June. Police and the government have pledged to bring all "culprits" to justice and to take "relentless enforcement action to bring the persons involved to justice."
Fox News' Paulina Dedaj, Brie Stimson and the Associated Press contributed to this report.