A young woman's murder has triggered some of the world's biggest protests in Hong Kong.

Over the past week, tides of people have flooded the streets of Hong Kong in a series of mass protests. Wearing black shirts, carrying banners and chanting, they flowed peacefully into the skyscraper-studded city’s urban centre.

Sunday’s demonstration was the largest so far. Police claimed the protest peaked with roughly 338,000 residents, but organisers and media put that figure closer to 2 million. Two million people from a population of just seven million, all united by one cause: opposition to an extradition law championed by Hong Kong’s Chief Executive Carrie Lam.

But what is it about the law, and this woman, that has millions taking to the streets? And how did a pregnant woman’s murder trigger it all?

The murder behind the Bill.

In 2017, Hong Kong national, Chan Tong-kai, killed his pregnant girlfriend, Poon Hiu-wing, 20, during a Valentine’s Day trip to Taiwan. According to Hong Kong English-language newspaper, The South China Morning Post, the 19-year-old told police he strangled her during an argument in their Taipai hotel room.

Chan reportedly claimed that Poon told him he wasn’t the father of her unborn child and showed him a video in which she was having sex with another man. Enraged, he hit her head against a wall and strangled her during a 10-minute tousle. He then put her lifeless body in a suitcase and went to bed. The following day he disposed of most of her belongings near the hotel, then travelled 15 train stops to a park on the city’s outskirts where he dumped her body. He then used her ATM card to withdraw HK$19,200 to pay his credit card bills.

Chan returned to Hong Kong, and was arrested when Poon’s remains were found on March 13. He confessed to the crime, but because Hong Kong doesn’t currently have an extradition agreement with Taiwan, he could not be sent there to face murder charges. Instead, the most authorities could charge him with was money laundering.

In February this year, Hong Kong officials mentioned the case as part of a proposal to expand extradition laws to include jurisdictions with which it currently doesn’t have a treaty. This includes Taiwan, Macau and China. And that’s where the protests begin.

So, why exactly are people protesting?

The possibility of suspected criminals being extradited to face trial in China, a place with a murky legal system and no human rights protections.

The government claims the law would stop Hong Kong from being a safe-haven for criminals (like Chan Tong-kai). But critics claim it could pave the way for China to target activists and political opponents, as part of its broader strategy to exercise control in the region.

Some context... Hong Kong is a former British colony that was handed to China in 1997. It now exists as an autonomous Chinese territory, or 'Special Administrative Region', meaning it has its own government, judicial and economic systems. In 2047, that special status expires, and it remains unclear what will happen then.

The uncertainty of that looming date, coupled with the increasing political influence of China, has many Hong Kong residents fearful that their autonomy could be under threat.

After all, the last few years has seen a spate of controversial government policies, including a new law that punishes those who disrespect the Chinese national anthem, and the disqualification of pro-democracy and pro-independence legislators from parliament in 2017.

The proposed extradition law has proven to be the tipping point for concerned Hong Kong citizens.

And so, in an effort to safeguard their freedom, they've marched on the city centre, in numbers not seen since the pro-democracy 'Umbrella Movement' protests of 2014.

How has the Hong Kong government responded?

During the first, smaller wave of protests on Wednesday, police fired tear gas, rubber bullets and water cannons at demonstrators who gathered outside Hong Kong government headquarters in an effort to stop a 'second reading' (debate) of the bill.

Dozens were injured in the clash, including 60 protesters and 22 police. Eleven people were arrested.

Chief Executive Lam, who became the territory's first female leader when she was chosen by the Election Committee in 2017,  responded to the issue during a television interview on Wednesday.

According to The South China Morning Post, Lam compared herself to a mother dealing with a spoiled child: "Lam said that if she gives in to every demand from her son, he would be spoiled, end up regretting getting everything he wanted, and he would blame her for not teaching him how to distinguish right from wrong," the paper wrote.

Her comments, and the response of police, inspired thousands more to join demonstrations over the weekend.

With pressure mounting, Lam suspended the bill on Saturday and issued a rare apology for "her government's work that has led to substantial controversies and disputes in society, causing disappointment and grief among the people".

But she has stopped short of agreeing to protesters' demands that the law be scrapped permanently and that she step down.

What happens now?

While the Chinese government openly backed Lam in a statement over the weekend, news of the protests has likely not reached Chinese citizens. The Chinese government will be doing everything it can to block media reports and social media chatter about what's unfolding in Hong Kong, amid fear it could inspire dissension among its own citizens.

But the rest of the world is watching closely to see what happens next. Will China press for the bill to be revived? Will that mean a new leader for Hong Kong? How long can the protesters maintain momentum, and at what cost?

Multiple international journalists have reported that protesters have pleaded with them to stay in the city, hoping the presence and scrutiny of foreign media will dissuade authorities from retaliating.

As 10 News reporter Hamish Macdonald told The Project on Monday, "One man came up to us and said, 'You're western journalists, please stay with us tonight. We're worried about a police crackdown. If they shoot us, if they hurt us, if they kill us, we want someone to have witnessed it."