Hong Kong CNN  — 

The Chinese military garrison in Hong Kong offered a rare public reaction in the face of taunts from protesters Sunday, as violence escalated across the city over the weekend.

Video from Hong Kong public broadcaster RTHK shows a yellow flag raised from atop a People’s Liberation Army (PLA) building in Kowloon Tong, in north Kowloon, warning protesters they could be prosecuted if they continued to approach the barracks. The flag appears to be similar to those used by police during protests.

Half a dozen personnel could be seen standing on top of the barracks shining flashlights at dozens of protesters below, who were aiming laser pointers and other lights at the building. The incident is believed to be the first known interaction between the PLA and protesters during 18 weeks of anti-government demonstrations.

Police sources told CNN that it was not the police on the roof of the building but was personnel from the PLA responding to the crowd. At no point did the soldiers venture from the garrison.

CNN has reached out to the office of the Hong Kong Chief Executive, the People’s Liberation Army in Hong Kong and the Chinese Defense Ministry for comment.

The interaction comes as protests intensified over the weekend following Hong Kong Chief Executive Carrie Lam’s use of emergency powers to ban face masks at public gatherings.

 A China Construction Bank (Asia) is vandalized in Causeway Bay district on October 6, 2019 in Hong Kong, China.

The city’s MTR subway network suspended all of its operations after demonstrators vandalized multiple train stations, setting fire to entrances and smashing ticketing facilities. Numerous mainland Chinese-owned banks and stores were also targeted by protesters.

Violent protests began Friday in opposition to the ban and stretched across the city throughout the weekend, with protesters throwing petrol bombs and police responding with pepper spray and tear gas. On Friday, a lone plain clothed police officer shot a 14-year-old boy in the leg after being attacked by protesters – the second time deadly force was used against protesters after an officer shot a protester during clashes on October 1.

Speaking Friday, Yang Guang, spokesman for the Hong Kong and Macao Affairs Office of China’s State Council, the country’s top law-making body, said the current unrest “cannot be endless.”

“More effective measures to stop the violence and ease the unrest” must be used, Yang said, adding the central government supports the anti-mask law.

‘A tipping point’

Use of colonial era emergency powers to institute the anti-mask law marks a significant escalation in the Hong Kong government’s handling of the now four-month long protests.

The emergency powers – which give the city’s Chief Executive effective carte blanche to make new laws as necessary in the instance of a severe breakdown of public order – have not been tested in court since Hong Kong’s return to China in 1997 and could be found unconstitutional under the city’s Basic Law, the de facto constitution, which guarantees rights such as public assembly and free expression.

Lam, the city’s leader, said at a news conference Tuesday her government had no plans to use emergency powers to enact new laws but did not rule it out.

Experts say the government’s move to invoke emergency powers as well as the protesters’ targeting of Chinese-owned business could move Hong Kong further toward a possible Chinese intervention.

“The very fact that the violence is intensifying in Hong Kong, both from the police against the protesters and the protesters are responding back in kind, I think, suggests that we are sort of reaching a tipping point in this,” said Malcolm Davis, senior analyst in Defense Strategy and Capability at the Australian Strategic Policy Institute. “They (Beijing) can’t let this go on indefinitely. They can’t let it continue to intensify.”

The Chinese military has had a presence in Hong Kong since the city was handed over from British to Chinese control in 1997. It is estimated that the PLA garrison houses around 6,000 soldiers.

Under the city’s constitution, the Hong Kong government can request the assistance of the garrison “in the maintenance of public order and in disaster relief.”

Police and government officials have repeatedly denied any need to call on the military, even as the protests have taken an increasingly violent turn.

Lam said at her Tuesday news conference she still feels strongly “that we should find the solutions ourselves,” and said the Chinese government also believes that Hong Kong should tackle the problem on its own. “But if the situation becomes so bad, then no options can be ruled out,” Lam said.

Lam said she did not “talk about business” with Chinese President Xi Jinping or central government officials during her trip to Beijing last Friday for national day celebrations.

In mid-August, China deployed large numbers of paramilitary personnel close to the border in Shenzhen. CNN teams on the ground saw uniformed members of the People’s Armed Police Force (PAP) with riot shields and batons, as well as numerous semi-militarized vehicles, stationed at the city’s Bay Sports Center.

A few weeks later China sent in fresh military troops to the Hong Kong garrison, saying it was part of the annual rotation of its personnel in and out of the territory.