Soldiers of the People's Liberation Army (PLA) perform drills during a demonstration at an open day at the PLA Ngong Shuen Chau Barracks in Hong Kong - Visual China Group

China publicly addressed the possibility of deploying the Chinese military to contain the public unrest in Hong Kong for the first time on Wednesday, suggesting that soldiers could be sent in at the request of Hong Kong officials.

China’s defence ministry said it is closely following the developments in the former British colony and pointed out that the government of Hong Kong has the legal right to call in Chinese military to maintain social order in the city.

The comments came at a press conference introducing China new defence white paper. Asked how the ministry would handle the situation in Hong Kong, a spokesman said only that “Article 14 of the garrison law has clear stipulations”.

Although he did not explicitly offer to send in the military, the comments mark a change in tone in recent days following alarming violence blamed on triad gangs in Hong Kong at the weekend.

Beijing has up until now suggested that Hong Kong authorities can deal with the growing unrest themselves, and has refrained from mentioning Article 14 and the highly controversial deployment of soldiers.

Article 14 of Hong Kong’s Basic Law, the city’s mini-constitution, states: “Military forces stationed by the Central People’s Government in the Hong Kong Special Administrative Region for defence shall not interfere in the local affairs of the Region.”

It goes on: “The Government of the Hong Kong Special Administrative Region may, when necessary, ask the Central People’s Government for assistance from the garrison in the maintenance of public order and in disaster relief.”

The People’s Liberation Army Hong Kong Garrison has been stationed in Hong Kong since Britain returned the sovereignty of Hong Kong to China in 1997. The troop is responsible for defence duties in Hong Kong and safeguarding national sovereignty.

Hong Kong government documents have estimated the number of troops is between 8,000 to 10,000 personnel.

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Beijing has been monitoring the situation in Hong Kong from a distance and remained hands-off during last month’s mass demonstrations. The news of mass demonstrations in Hong Kong was downplayed in Chinese media.

The central government offered moral support to the Hong Kong government and its police force handling weeks of social disorder.

But Beijing’s response has turned tougher this week after the protesters besieged the central government office in Hong Kong, which is a symbol of Beijing’s sovereignty over the city. The vandalism has irked Beijing.

Chinese media aired images of a defaced national emblem on state broadcast news on Tuesday, and state newspapers run editorials condemning the vandalism.

They referred to the radical protesters as anarchists who directly challenge China’s governing framework in Hong Kong and the central government’s authority.

Dr Willy Lam, China expert at the Center for China Studies at the Chinese University of Hong Kong, said the change in tone was a warning to protesters.

He added: "Politically, if the PLA soldiers are deployed to Hong Kong, that will mean the end of the “one country, two systems” framework to govern Hong Kong. Hong Kong will be another Chinese city with the PLA troops on the ground."

China on Wednesday also blamed the US behind the public unrest in Hong Kong and warned against foreign interference, after Sunday’s vandalism.

“We can see that US officials are even behind such incidents,” said Chinese Foreign Ministry spokeswoman Hua Chunying at a regular press briefing on Tuesday.

The Chinese foreign ministry has reiterated that Hong Kong’s affairs are China’s internal affairs.

Hua, asked about criticism of violence by the United States and Hong Kong’s former colonial ruler, Britain, said China would not tolerate any interference.

“The US should know one thing, that Hong Kong is China’s Hong Kong, and we do not allow any foreign interference,” she said.

“We advise the US to withdraw their black hands.”

Mr Lam said: "There's a conspiracy theory now that the US is behind the public unrest supporting the protests in Hong Kong. It's a justification for Xi Jinping to use a draconian measure - deploying troops - to contain the public unrest in Hong Kong."