China is sending a strong signal of force to Hong Kong, with a heavy military presence spotted near the border as protests in the financial hub heat up.
Hundreds of armoured vehicles appeared in the city of Shenzhen near the border between mainland China and the Hong Kong special administrative region on Monday (local time).
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Communist Party-aligned tabloid the Global Times reports the armoured personnel carriers, trucks and other vehicles are in the city for military exercises.
But experts believe it's a show of force as tensions between authorities and protesters in Hong Kong skyrocket.
Waikato University professor of international law Alexander Gillespie told Newshub China is sending a signal to the protesters.
"Chinese authorities have already warned the protesters that they are playing with fire and if the protests keep escalating, and they do seem to be escalating at the moment with what's happening in the airport, it is possible at some point that the Chinese authorities, the military could intervene.
"You must remember that China already has a garrison in Hong Kong of I think 600 men, but this would be of a different magnitude."
Prof Gillespie said it would take a big event like a death, or the prolonged closure of the airport, to force intervention.
"If they're gonna intervene they're going to come across the border. That would be the expected way to do it. The question is how long China holds off for, before it gets to that point and unless the protests deescalate at some point China will intervene."
China will have to be careful of how it conducts the intervention though, to avoid a repeat of Tiananmen Square, where at least hundreds of protesters were killed.
"China's also got to be very careful because aside of the human rights debates there's the economic value of Hong Kong because if it's destabilised it would lose a lot of monetary value," Prof Gillespie said.
The protests began as a fight against an extradition treaty between Hong Kong and China, but have continued despite the Bill's suspension on June 15.
They're asking for the resignation of Hong Kong chief executive Carrie Lam, an independent inquiry into police behaviour and the complete withdrawal of the extradition Bill.
Protesters caused chaos inside the Hong Kong airport on Monday afternoon (NZ time), forcing flight cancellations.
The airport has since reopened, but concerns about what will happen next remain.