Hundreds of members of China's People's Armed Police have been seen conducting exercises at a sports stadium in Shenzhen, as the US expressed concern they could be deployed in nearby Hong Kong to break up protests.
But Western and Asian diplomats in Hong Kong said Beijing has little appetite for rolling the PAP or the People's Liberation Army onto Hong Kong's streets.
On Thursday men in fatigues could be seen in a stadium and shouts and whistles could be heard by a Reuters journalist. The stadium is next to a retail complex and shoppers were milling around the area, although the entrances to the stadium were closed.
Parking spaces at the stadium were filled with more than 100 dark-painted paramilitary vehicles, including troop trucks, armoured personnel carriers, buses and jeeps. Two vehicles carried water cannons.
Troops marched in and out of the stadium, some in fatigues, some in black T-shirts and camouflage trousers. The floor of an indoor area visible through an open gate was lined with mats and rucksacks.
Chinese state media have made several mentions of exercises in Shenzhen.
The Global Times, a nationalistic tabloid run by the ruling Communist Party's official People's Daily, published a slick video early this week showing columns of trucks and armoured personnel carriers rolling through the city.
The paper said the vehicles belonged to the People's Armed Police and had gathered for "apparent-large scale exercises." Its editor, Hu Xijin, described it on Twitter as "a clear warning to rioters in Hong Kong."
The Communist Party's official People's Daily newspaper said on the social media platform Weibo that the force handles incidents that include riots and terrorist attacks.
On Thursday the US State Department said it was deeply concerned about reports that Chinese police forces were gathering near the border with Hong Kong and urged the city's government to respect freedom of speech.
Still, diplomats in Hong Kong said they believe Chinese leadership is well aware that moving mainland forces into Hong Kong would shatter international faith in the "one country, two systems" model at the heart of Hong Kong's role as a global financial hub, and would swiftly lead to sanctions.
"We are seeing an escalation in the posturing that appears designed to send messages to both Hong Kong and the mainland ... but we are confident we are still in the realms of propaganda here," one senior Western envoy told Reuters, speaking on condition of anonymity.
"The trucks aren't about to roll at this point."