HONG KONG - Major-General Tan Benhong, the commander of the People's Liberation Army (PLA) in Hong Kong, was a picture of uniformed calm as he shared champagne toasts with Chinese officials on Wednesday at local celebrations marking China's national day.
The streets surrounding the bash at the Hong Kong Convention Centre presented a starkly different scene, as thousands of protesters escalated the most sustained push for full democracy since China took Hong Kong back from Britain in 1997.
As the protests enter their second week amid fresh signs of street violence, some demonstrators and ordinary Hong Kong citizens fear Maj-Gen Tan's troops could eventually be ordered to crush a movement unthinkable on the mainland.
Thorny political, legal and strategic realities make any such involvement of the PLA exceptionally difficult, however, and Hong Kong's 27,000-strong police force is expected to remain in charge for the time being.
Government advisers and experts believe leaders in both Beijing and Hong Kong understand the immense political costs of ordering the PLA out of their barracks, ending at a stroke Hong Kong's vaunted autonomy under the "one country-two systems" formula under which Britain agreed to hand over the Asian financial hub.
Foreign diplomats are monitoring developments closely, noting moves in recent months to upgrade PLA facilities in Hong Kong and unconfirmed reports of anti-riot drills being staged at both urban and rural bases.
The garrison comprises between 8,000 to 10,000 personnel, mostly infantry troops, spread between bases across the border in Shenzhen and in Hong Kong, envoys estimate. It includes a small naval and air-force attachment.
"I think that (Hong Kong) policymakers at the highest level ... are fully aware in that if the PLA were deployed, in the eyes of the world it would be the end of one country-two systems," said Ms Regina Ip, an adviser to embattled Hong Kong leader Leung Chun Ying and a former security chief.
"It would cause tremendous damage," she said, noting that the local government officials had repeatedly stressed that local police - equipped with paramilitary anti-riot units - were fully capable of dealing with the unfolding situation.
A Hong Kong-based mainland security academic said he believed Beijing was also acutely aware of the risks of using the PLA in Hong Kong.
"I am sure the leadership in Beijing knows that any such involvement would involve massive political costs," he said, speaking on condition of anonymity given the sensitivity of discussing PLA operations.
"For that reason, the PLA in Hong Kong is maintained largely as a symbolic presence."
Foreign diplomats watching developments remain unsure of the precise political threshold that must be crossed for Beijing to unleash the troops.
Their presence in Hong Kong, after all, has been one of the most sensitive elements of the handover, fuelled by deep local memories of the 1989 army crackdown on protesting students in and around Tiananmen Square in Beijing - an event still commemorated annually in the city.
The Chinese military is housed in 19 urban and rural sites inherited after the British folded up the Union Jack on what had been a major military staging post of the British empire and a vital Cold War-era listening post.
The bases, dotted strategically across Hong Kong island, Kowloon and the New Territories, include the old British Tamar headquarters building in Admiralty, now next door to the government's new offices - and the epicentre of the current demonstrations.
The building was recently refurbished, along with other sites, and is now topped with a red neon star. Most of its offices are thought to be occupied, some for the first time.
A large domed surveillance camera sits perched above a corner over one of the main throughfares leading to Hong Kong's glittering Central financial district.