Hong Kong has vowed to push ahead with controversial changes to its extradition laws, which will allow wanted criminal suspects to be transferred to mainland China to face trial.

But a number of foreign governments, including the United States, United Kingdom and Canada, have warned the new laws could threaten the territory's autonomy and status as an international business hub.

So what exactly has been proposed, do foreigners need to be worried, and what does the Australian Government say?

What changes have been proposed?

Hong Kong currently has extradition agreements with 20 jurisdictions across the world, including Australia.

But the Hong Kong Government is now seeking to change the law to enable extradition to any jurisdiction with which it doesn't have an agreement.

That includes Taiwan, Macau and mainland China, which has been excluded from agreements in the past because of concerns over its judicial independence and human rights record.

Hong Kong's chief executive, Carrie Lam, says without the changes, Hong Kong risks becoming a haven for criminals from the mainland.

The laws will make it easier for Hong Kong to send criminal suspects to mainland China. ( AP: Vincent Yu )

Why is this happening now?

When the former British colony was transferred to China in 1997, experts and government officials warned it would need a extradition deal with mainland China.

But very little progress has been made since then.

Now officials are seizing on the recent case of Chan Tong-kai, a Hong Kong man who admitted to Hong Kong police that he killed his girlfriend during a trip to Taiwan, to push for swift changes.

Because Hong Kong and Taiwan don't have an extradition agreement, he has not been sent to Taiwan to face charges there, and is now in jail in Hong Kong on lesser money-laundering charges.

Why are people protesting?

Many people in Hong Kong believe the changes will significantly compromise the territory's legal independence, long viewed as one of the key differences between Hong Kong and mainland China.

Critics believe Hong Kong residents could get trapped in China's murky judicial system, in which political opponents have been charged with economic crimes or ill-defined national security transgressions.

Once charged, they believe the suspects may face unfair proceedings in a system where the vast majority of criminal trials end in conviction.

What have foreign governments said?

The United States says it's gravely concerned about the proposed amendments.

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"The United States shares the concerns of many in Hong Kong that the lack of procedural protections in the proposed amendments could undermine Hong Kong's autonomy and negatively impact the territory's longstanding protections of human rights, fundamental freedoms and democratic values," a spokeswoman for the US State Department, Morgan Ortagus, said.

"We're also concerned that the amendments could damage Hong Kong's business environment and subject our citizens residing in or visiting Hong Kong to China's capricious judicial system."

The UK and Canada are also concerned for their citizens in Hong Kong, as well as the territory's "international reputation".

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A joint statement from UK Foreign Secretary, Jeremy Hunt, and Canada's Minister of Foreign Affairs, Chrystia Freeland, said "the continued erosion of the 'One Country, Two Systems' framework puts at risk Hong Kong's long-established special status in international affairs".

"We believe that there is a risk that the proposals could impact negatively on the rights and freedoms set down in the Sino-British Joint Declaration," the statement added.

"It is vital that extradition arrangements in Hong Kong are in line with 'One Country, Two Systems' and fully respect Hong Kong's high degree of autonomy."

What about Australia?

Protesters walked down Elizabeth Street in Sydney over the weekend. ( Reuters: Alison Bevege )

A spokesperson for Foreign Minister Marise Payne said the Australian Government was taking "a close interest" in the proposed amendments, "including to ascertain any impacts on Australian residents".

"The Australian Consul-General in Hong Kong has raised the issue with senior levels of the Hong Kong Government," the spokesperson said.

Labor's spokesperson for foreign affairs, Penny Wong, said she was also concerned about the message the changes would send to foreign companies operating in Hong Kong.

"Those are matters that I would assume and I would hope that the Hong Kong authorities would take into account," she said.

"I also hope that the Australian Government would be expressing these views about the potential implications for Australians from these proposals."

What exactly is Hong Kong's relationship to mainland China?

Hong Kong was a British colony that was returned to China in 1997 under the framework of "One Country, Two Systems".

The agreement guaranteed Hong Kong the right to retain its own social, legal and political systems for 50 years.

As a result, residents of the semiautonomous territory enjoy far greater freedoms than people on the mainland, such as the freedom to protest or publicly criticise the Government.

Nevertheless, the Communist Party exerts influence on the Hong Kong Government.

Hong Kong voters are not allowed to directly elect their chief executive — Ms Lam was elected in 2017 by a committee dominated by pro-Beijing elites and is widely seen as the Communist Party's favoured candidate.

The Legislative Council, Hong Kong's Parliament, also includes a sizable camp of pro-Beijing officials.

Have freedoms been eroding?

Those in Hong Kong who anger China's central government have come under greater pressure since Chinese President Xi Jinping came to power in 2012.

The detention of several Hong Kong booksellers in late 2015 intensified worries about the erosion of Hong Kong's rule of law.

The booksellers vanished before resurfacing in police custody in mainland China. Among them, Swedish citizen Gui Minhai is currently being investigated for leaking state secrets after he sold gossipy books about Chinese leaders.

Chinese state media said foreign forces were behind the protests over the weekend. ( ABC News: Kathryn Diss )

In April, nine leaders of a 2014 pro-democracy protest movement known as the "Umbrella Revolution" were convicted on public nuisance and other charges.

In May, Germany confirmed it had granted asylum to two people from Hong Kong who, according to media reports, were activists fleeing tightening restrictions at home.

It was the first known case in recent years of a Western government accepting political refugees from Hong Kong.

So what's next for the extradition bill?

Ms Lam has vowed to move forward with the legislation despite massive protests.

Debate will resume on Wednesday and the bill could be passed into law by the end of June.

AP/Reuters