Hong Kong is the world's gateway to China,
but it's more than that.
It's China's gateway to the world, especially when it
comes to what makes the city really tick - finance.
Hong Kong is run under a different set of rules
to the rest of China known as One Country Two Systems.
It has its own currency, an independent legal system,
and a quasi-democratic government that -
in theory at least - operates under a high degree
of autonomy.
However, three months of increasingly violent
demonstrations have exposed the fault lines in the system
and are forcing Beijing to face an uncomfortable question.
Just how important is Hong Kong?
When the territory was handed over from the British
to the Chinese in 1997, Hong Kong's economy was equal
to about a fifth of China's.
Spectacular growth in China over the two decades since then
have shrunk that to the equivalent of less than three
per cent.
Surely, China could live without that if it needed to.
The truth isn't that simple.
Capital controls on the renminbi mean
that if a Chinese company wants to expand overseas,
it needs to raise money outside mainland China.
At the moment, a third of all dollar bond
issuance by Chinese companies happens in Hong Kong.
Could companies raise foreign currency in New York or London?
In theory, yes, but the lack of knowledge and familiarity
would make it a whole lot more difficult for many of them.
It's a similar story when it comes to the stock market.
Three-quarters of all funding from offshore IPOs
is raised in Hong Kong, where investors
are comfortable putting their money
into mainland-based companies.
With the Hong Kong currency pegged to the US dollar,
that means Chinese companies can get ready access
to some of the deepest capital markets in the world.
Chinese companies could list elsewhere,
but a highly liquid market on their doorstep
makes Hong Kong an easier and more attractive option.
It isn't just companies looking to expand overseas
that want foreign investment.
Hong Kong's Stock Connects with markets
in Shanghai and Shenzhen allow foreign investors
to put their money into Chinese companies
without worrying about China's capital controls, which could
stop them getting back out.
Hong Kong may have become politically unstable
and a source of discomfort for the government in Beijing.
But if China was to dismantle the firewall
between the mainland and Hong Kong,
it's not just the Asian financial hub
that would suffer.
Corporate China would also find itself left in the lurch.