Hong Kong protests: How could China intervene?
Hong Kong has experienced weeks of unrest now, sparked by opposition to an extradition bill, with increasing outbreaks of violence and strikes causing major disruption.
The Chinese government has strongly criticised the protesters, but many are wondering whether it will eventually lose patience and take more direct action.
What legal options does Beijing have to intervene, and could we ever see Chinese military action in Hong Kong?
Could China send in the army?
The Basic Law - Hong Kong's mini constitution since the UK handed the territory back to China in 1997 - is very clear.
Unless China declares an all-out state of emergency or war in Hong Kong, Chinese military intervention can only come at the request of the Hong Kong government, and for the "maintenance of public order and in disaster relief".
But most analysts say at this stage is almost unthinkable that PLA troops will be seen in Hong Kong.
"It would bring dramatic change to the structural and economic environment," said Prof Ivan Choy of the Chinese University of Hong Kong. "The consequences of [such a] move would be far reaching."
Dr Choy says such a move would shatter faith in the "one country, two systems" model that has governed Hong Kong since the handover, possibly irreparably.
The PLA has had about 5,000 personnel based in Hong Kong since the handover, which Adam Ni, a China researcher at Macquarie University, describes as a largely "symbolic presence of China's sovereignty".
But on 31 July, the garrison broke its silence on the protests, releasing a video which included footage of soldiers shouting - in Cantonese - "all consequences are at your own risk", troops advancing against protesters and a scene where police held up a banner with the words "Stop charging or we use force", a warning commonly used by Hong Kong police during unrest.
Dr Choy says Beijing has been trying to "continually remind people in Hong Kong that there is the possibility [of military force]".
"They don't want to rule out the possibility of such a move... [hoping] this will create some sort of psychological pressure."
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So far, China's top policy office on Hong Kong has said it has full faith in the police to handle the unrest. But spokesman Yang Guang also warned that "those who play with fire will perish by it" and protesters should not "mistake restraint for weakness".
Mr Ni said the political risk for the Chinese government, both domestically and internationally, of military intervention was simply too great, and could indeed worsen the crisis.
"Any military response short of overwhelming force would lead to further resistance," he told the BBC.
Can China intervene politically?
Hong Kong's political set up is not fully democratic - which has sparked resentment among protesters, and led to calls for democratic reform.
China has arguably also made a number of political interventions, and that has been a driving factor behind recent protests.
Hong Kong's parliament, the Legislative Council, is tilted in Beijing's favour and is only partly democratic - about half the seats are directly elected by voters.
Meanwhile, the chief executive is chosen by a largely pro-Beijing election committee - which in turn is chosen by only 6% of the electorate. As a result, critics say Hong Kong's leaders answer to Beijing, rather than Hong Kong's electorate.
Carrie Lam was elected in 2017, and it was she who introduced the extradition bill that sparked the new protests, becoming a focus of the anger herself.
Prof Dixon Ming Sing of the Hong Kong University of Science and Technology says Beijing has "done a lot to show its power... adamantly refusing the resignation of Carrie Lam and refusing to [let her] formally withdraw the bill".
"If Beijing wants her to resign, can it be done? Absolutely," he said. "But I think Beijing doesn't want to do so because it wants to show it cannot be shaped by public opinion."
Of course, even if Ms Lam did leave her post, her replacement would also have to have Beijing's backing.
And other political moves in Hong Kong in recent years - including opposition MPs being disqualified for failing to say the oath of allegiance properly, and a law proposing banning disrespect of the Chinese national anthem - have made it clear that the authorities in Hong Kong are keen to counter anti-Beijing sentiment.
Could China target individual activists?
The protests were trigged by an extradition bill, which critics feared could have been used by China to remove political activists to the mainland, where they would face almost certain conviction.
Carrie Lam has said the bill is now dead, but even without it, there have been enough reports of China bypassing such laws to detain Hong Kong citizens for protesters to be worried.
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Gui Minhai, who ran a bookstore in Hong Kong selling books critical of the Chinese government, is one of the most high-profile cases. He went missing in Thailand in 2015, before reappearing in China where he was detained over a fatal car accident in 2003.
A Chinese court sentenced him to two years in prison. He was released in 2017 but was allegedly seized again the following year while on a train in China. He has not been seen since.
And even if activists themselves don't fear arrest, some may fear repercussions for any family members on the mainland.
However despite fears of direct intervention in Hong Kong, Beijing's most effective tool to calm the unrest is likely to be a subtle but potent economic one.
Hong Kong is an economic powerhouse, and has remained so since handover in part because of the special status it has enjoyed as part of the handover agreement. But cities on the mainland like Shenzhen and Shanghai have rapidly caught up since 1997 nonetheless.
If Hong Kong continues to challenge Beijing's authority, the government could further redirect investment and trade towards the mainland, squeezing Hong Kong's economy and making it far more reliant on Beijing's goodwill.