The Chinese government has released footage that appears to show military vehicles driving towards the Hong Kong border.
The short clip shows a series of roughly two dozen green armoured fighting vehicles entering a "service area" in a row and riding down a highway, purportedly towards Shenzhen, the mainland city bordering the territory.
The state-run People's Daily did not comment on the purpose of the vehicles, but noted that the People's Armed Police are in charge of "handling riots, turmoil, seriously violent, criminal activities, terrorist attacks and other societal security incidents".
The post coincided with a statement from Chinese authorities vowing to crack down on Hong Kong protesters and likening the demonstrations to "terrorism".
"Radical Hong Kong protesters have repeatedly used extremely dangerous tools to attack police officers," said Yang Guang, a spokesman for the Chinese government's Hong Kong and Macau Affairs Office, in remarks translated by Chinese state media. "The first signs of terrorism are starting to appear."
He said the protesters' "violent crimes" must be dealt with "resolutely" and "without mercy".
"If we allow these types of terrorist activities to continue, then Hong Kong will slide into a bottomless abyss," China's liaison office in Hong Kong added on Monday.
Mainland Chinese authorities have remained in barracks since the protests began in June, leaving Hong Kong's police force to deal with them.
The movements of the military vehicles are not an isolated incident. Last week, Chinese police in Shenzhen carried out a large-scale anti-riot drill involving 12,000 officers in which they demonstrated a newly-developed tear gas to quell protesters.
At the start of August, Chinese forces congegrated abruptly at the border with Hong Kong, alarming the White House.
Last night, mayhem ensued in Hong Kong's busy airport after thousands of protesters stormed its main terminal, disrupting operations and freezing flights.
More than 5000 protesters streamed into one of the world's busiest transport hubs and quickly transformed the arrivals hall into a sea of black.
Airport staff advised passengers to leave the airport for their own safety, but traffic outside was at a near standstill, and public transportation was clogged. Some passengers and departing protesters opted to walk.
TIANANMEN 2.0?
Some social media users have compared the footage to that of the Tiananmen Square crackdown of 1989, suggesting a similar catastrophic event may unfold in Hong Kong.
But analysts say this is unlikely, noting that the potentially economic and political consequences will deter Beijing from any overt on-the-ground intervention.
"Beijing wants to use the threat of sending in the PLA, or other direct intervention, to try to scare off the protesters," said Ben Bland, research fellow at the Lowy Institute. "But given the high level of operational risk — and the reputational and economic risks to China — sending in the PLA would be a dangerous move."
"Even 100 soldiers in the central business district, if they suddenly appeared on the front page of all major newspapers, would have a very chilling impact on multinational companies based in Hong Kong," Willy Lam, adjunct professor at the Chinese University of Hong Kong told CNN.
According to analyst Wu Qiang, a former politics lecturer at Tsinghua University in Beijing, China learned its lessons from the 1989 crackdown as it conducted numerous "exchanges" with police forces in Europe and the United States.
"A large part of this was exchanges on how to deal with political riots and peaceful protests," Wu said. "The Chinese regime has no experience of suppressing riots in a free society."
Earlier this month, Beijing admitted Hong Kong was facing its worst crisis since the territory was handed over from Britain to China in 1997.
"Hong Kong's crisis … has continued for 60 days, and is getting worse and worse," Zhang Xiaoming, the head of the Hong Kong and Macau Affairs office, said during a meeting in Shenzhen.
"Violent activities are intensifying and the impact on society is spreading wider. It can be said that Hong Kong is now facing the most severe situation since its handover."