Hong Kong is widely considered Asia's economic and financial powerhouse, with one of the most free and competitive economies in the world.
And while the city is technically part of China, there's a number of features that make it stand out from the Mainland.
Hong Kong is a Special Administrative Region of the People's Republic of China.
This means it's in China, but operates under its own set of rules and regulations, with the exception of defense and foreign affairs.
This is laid out in what's called the Basic Law, Hong Kong's constitution and a national law for China.
The high degree of autonomy that Hong Kong enjoys, along with its status as an economic powerhouse, makes it unique compared to the rest of the mainland.
These differences are encapsulated by the “one country, two systems” principle, which means each system has its own set of government, legal, financial, economic regulations and even separate trade relations with other nations.
So what are some of the key distinctions between Hong Kong and mainland China?
Well, despite sharing multiple air, sea and land links, like the Hong Kong-Shenzhen border for instance, you'll need to go through passport control when moving between Hong Kong and the mainland, regardless of nationality.
In fact, sometimes it's more seamless crossing between two separate countries.
Take going between France and Germany for example.
They have no controls because they're both part of the Schengen Area.
Hong Kong residents are also issued passports that are different from their Chinese counterparts.
And if you have a passport from, say the U.S., Germany or more than 100 other countries, you can enter Hong Kong without a visa.
But visitors from most countries will need a visa to enter Mainland China.
China's well-known internet blocks, which prevent you from accessing the likes of Google and Facebook, aren't in place here in Hong Kong.
Freedom of expression is well protected by the Hong Kong Bill of Rights.
No political views can be blocked online, and government licenses aren't required to run a website.
That's not the case in most of China.
Here they use the Hong Kong dollar.
While in China, they use the Yuan.
And while China's government is heavily involved in the running of its economy, Hong Kong's is ranked as the world's freest, thanks to its government integrity, and trade and monetary freedom.
But that could change in 2047.
So why the expiration date? And why is this relationship so unique?
It all started in 1842.
Hong Kong was surrendered to the British "in perpetuity", after the Qing dynasty of China lost the First Opium War.
A second territory, a part of the Kowloon peninsula, was ceded by Qing China to the British in 1860 after the Second Opium War.
Finally, the New Territories were leased to the U.K. for 99 years rent-free in 1898.
In the 1980s, China broke its silence and called for the "reunification of the Chinese nation".
After lengthy negotiations, both countries agreed Hong Kong would revert to Chinese rule in 1997, the same year the 99-year lease on the New Territories expired.
British rule of Hong Kong, which included Hong Kong Island, Kowloon and the New Territories, ended on July 1 1997.
Despite being handed back to China, the Sino-British Joint Declaration guarantees Hong Kong's political and economic systems would remain unchanged for 50 years.
That includes freedoms such as the right to assemble and demonstrate, the right to free speech and a free press.
What will happen in Hong Kong after 2047 is anyone's guess.
As you can imagine, that could get complicated.
See, in past decades, Hong Kong thrived and rose to become one of Asia's financial powerhouses, ultimately becoming a hub for western companies looking to do business in China.
China's opening of its economy in 1978 propelled the country to become the world's second-largest economy behind the U.S., drawing hundreds of millions out of poverty in the process.
And while Hong Kong was strategically well-positioned to benefit from China's economic boom, it was a double-edged sword.
Hong Kong, which was traditionally a crown-jewel for China, at one point representing 27% of the Chinese economy back in 1993, now represents less than 3%.
In fact, Hong Kong's economy was recently surpassed by the city of Shenzhen, a booming tech city just across the border in Mainland China.
So Hong Kong is now much less significant to China's overall economy.
And while Hong Kong is supposed to remain an autonomous region until 2047, some say China doesn't want to wait that long.
In recent years, China has tightened its embrace of Hong Kong, not just symbolically, but through massive infrastructure projects too.
For one, there's the Greater Bay initiative.
It hopes to combine the cities of Guangzhou and Shenzhen in Southern China with the likes of Hong Kong and Macau to create one massive area that could rival San Francisco, New York and Tokyo's bay areas.
The Greater Bay Area is home to more than 65 million people.
This new $20 billion dollar bridge is an example of that initiative.
It's the longest sea-crossing bridge in the world, connecting Hong Kong to the Mainland.
Some critics have actually linked the bridge to an umbilical cord between Hong Kong and China, saying that it's a symbolic way for China to exert more influence over Hong Kong.
And there's this new controversial high-speed rail, which allows Mainland Chinese officials to exercise jurisdiction in Hong Kong for the first time.
The city has seen an influx of mainlanders, around one million since 1997, accounting for 90% of Hong Kong's population growth.
This influx has fueled some resentment, with some locals blaming them for pushing up property prices and driving down wages.
In several instances, Hong Kongers have resisted China's influence.
In 2003, hundreds of thousands protested against proposed national security legislation critics said would erode the coastal city's freedoms.
In 2014, tens of thousands of people protested China's influence over Hong Kong's elections.
This gave birth to the Umbrella Movement, named after the umbrellas protesters used to shield the pepper spray used by police.
In 2017, the Chinese Foreign Ministry declared the Sino-British Joint Declaration no longer had any significance, though it was unclear whether the attack was on British involvement in Hong Kong or the core principles in the document.
Britain says the document is still a valid treaty.
And in 2019, more than half a million protestors flooded the streets to protest an extradition bill that would allow fugitives to be transferred to places with which the city has no extradition arrangements, including mainland China.
Recently, Hong Kong fell two spots in the Economist Intelligence Unit's Global Democracy Index landing at 73rd place on a list of 167, tying with Senegal and below Mexico.
China, meanwhile, rose nine places to 130.
Hong Kong's autonomy and economic freedom have been key to its rise as a global economic hub.
But being seen as the gateway to China has also been imperative.
Keeping that balance between the two is something Hong Kong will continue to contend with, particularly as it edges closer to 2047.
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