Just food for thought, but it really depends on who leads a revolution and how much planning they put in. Having troops garrisoned in HK doesn't mean they can't fight a guerilla war, as someone pointed out, and it doesn't mean that the troops can't be caught with their pants down, which isn't all that unlikely. Lack of readiness is something occupation forces constantly have to look out for and Chinese troops are not exactly known for their readiness.
Let us suppose that some half-Chinese/half-British HKer did a stint with the Royal Marines or the SAS before the '97 transfer. This person would have had access to some of the best military training in the world and be thoroughly cemented in Western thought. He doesn't lead the revolution, he just signs on to help keep the zealous revolutionaries grounded in practical thought. To build a single SAS-type squadron takes 18 months. That is about 150-200 men. This can be done in warehouses and any other abandoned area in an urban environment, though there will need to be need to wilderness training, and a lot of it.
Considering their proximity to the intended target, the garrisoned troops, actually obtaining intelligence about the target is going to be easier. A few pro-democracy revolutionaries pose as communist hardliners and are able to get in on a visitor basis. They ID their tagets: comm. stations, vehicles, aircraft, armories. 150-200 men working around the clock for months to make mines and explosives (and buying them off the black market) means your going to have a substational stockpile.
Gvien that they have the element of surprise, the needed intelligence, the upper hand in training, and the ability to wait for a point of low readiness, the garrison of Chinese troops is quickly going to become a lot of hostages. What isn't destroyed is going to become equipment for this squadron.
Now, moving ahead, let us focs on the Chinese reponse. Troop movements are going to be slow; weeks or months. Probably months. In any case, this is not something they would have expected and they have to move troops from other locations and organize them to prepare an invasion. Tack on more time.
Air power is a different issue. Planes can be deployed with the space of hours, but an actual strategy will take days to develop and more likely weeks. They have zero intelligence on anti-air capability and have to choose which targets to hit. You can also bet that there will be resistance to bombing HK at all; it's a cash cow. Taking weeks to finally launch an air strike is a strong possibility.
It goes back to a period of preparation. Did these revolutionaries prepare neough before hand? Preparing for an invasion without an army means that nukes are almost a prerequisite. Here is how easy it is to obtain them: Back in the mid-90s, the Russian mafia nearly sold a fully-loaded nuclear submarine (with the warheads onboard) to two US federal agents posing as middle men for a Columbian drug-lord, all for a paltry $15 million. The agents, being escorted by a Russian immigrant to the US acting as the middle man for the mafia, were allowed ot meet the crew of the submarine and examine it for tthemselves. The Russian mafia will just about do business with anyone.
Let us assume that the revolutionaries have a large support base among the younger set and have collected donations for a charity that acted as a front for the armed revolution. That is quite a bit of money to work with, so they buy two subs and the Russians teach them how to use them and even offer maitenance equipment. China is planning an invasion and a video tape comes in to international news agencies showing an uninhabited island going up in a mushroom cloud. HK now announces they have nukes.
I have to disagree with the comment above that nukes is going to get them labeled "terrorists" and make them instant pariahs. It solely depends on how they explain themselves and how they use them. It they show the restraint of a reponsible nation-state and illustrate the obivousness of not having the armed forces to repel an invasion, they have wiggle-room. It is a bargaining chip.
Taiwan has little reason to substationally support them, other than some indirect morale support. South Korea, depending upon it's relations with China, might have reason to deal with HK under the table. Military advisors are all you can expect though.
That just about leaves Israel, Russia, UK, and the US. Israel has the cajones to help, but no direct interest. Russia is already helping and is probably going to take every opportunity to get more money out of them. The US can be expected to take a "neutral" stance. The CIA might assist in some small way, but were trying to take the free-tade route as a method to get rid of the Communists. The UK is more likely to assist. They still have ties to it and even unofficially, there are going to be people with training and credentials willing to consult.
That leaves the catalyst. This revolution didn't happen over night. China probably made a hardline shift somewhere along the way that made HKers very mad. I'll deal with the Chinese forces and food issue later.
