Hong Kong's Legislative Council will start discussions on Wednesday on the amendments to the Fugitive Offenders Ordinance, which would allow suspected criminals to be sent to China for trial

Several thousand people jammed Hong Kong's streets on Sunday in the biggest rally in more than a decade, to thwart a proposed extradition law that would allow suspects to be sent to mainland China to face trial.

Sunday's outpouring was widely expected to raise the pressure on the administration of Hong Kong Chief Executive Carrie Lam and her official backers in Beijing.

Organisers said that their initial estimates put the turnout at well over half a million people, adding that it outstripped a demonstration in 2003 when over five lakh people hit the streets to challenge the Government’s plans for tighter national security laws. Those laws were later shelved and a key government official was forced to resign.

Mr. Lam is yet to comment on the rally, which followed weeks of domestic discontent growing amid official concern from the U.S., the European Union and foreign business lobbies that the changes would dent Hong Kong's vaunted rule of law and freedoms.

The unusually broad opposition to the extradition bill displayed on Sunday came amid a series of government moves to deepen links between southern mainland China and Hong Kong. The former British colony was handed back to Chinese rule in 1997 amid guarantees of autonomy and various freedoms including a separate legal system, which many diplomats and business leaders believe is the city's strongest remaining asset.

While the police is yet to issue their own estimate of the protest size, tens of thousands reached the Legislative Council in the Admiralty Business district, with the starting point in Victoria Park crowded with thousands more still waiting to join the march.

Chants of “no China extradition, no evil law” echoed through the high-rise city streets, while other marchers called for Mr. Lam and other senior officials to step down. One protester held a sign reading “Carry off Carrie”, while another declared “Extradite yourself, Carrie.” Another sign said ”let's make Hong Kong great again”, with a photo depicting U.S. President Donald Trump firing Lam.

Debates will start in Hong Kong's Legislative Council on Wednesday on the amendments to the Fugitive Offenders Ordinance. The bill could be transformed into a law by the end of June.

Mr. Lam has tweaked the amendments but refused to pull the bill, saying it is vital to plug a long-standing “loophole”. She has also said that speedy action is needed to ensure that a Hong Kong man suspected of murdering his girlfriend can be sent to Taiwan for trial.

Protests against the bill were also planned on Sunday in 26 cities globally, including London, Sydney, New York and Chicago.

The amendments would simplify case-by-case arrangements to allow extradition of wanted suspects to jurisdictions, including mainland China, Macau and Taiwan, beyond the 20 that Hong Kong already has extradition treaties with.

Opponents of the bill question the fairness and transparency of the Chinese court system and worry about Chinese security forces contriving charges.

Chris Patten, the last British governor of Hong Kong, said on Thursday that the bill would “strike a terrible blow...against the rule of law, against Hong Kong's stability and security, against Hong Kong's position as a great international trading hub”.

Foreign governments have also expressed concern, warning of the impact on Hong Kong's reputation as an international financial hub, and noting that foreigners wanted in China risk getting ensnared in Hong Kong.

Concerns were highlighted on Saturday with news that a local high court judge had been reprimanded by the Chief Justice after his signature appeared on a public petition against the bill.

According to a previous report by the Reuters, several senior Hong Kong judges were worried about the changes, noting a lack of trust in mainland courts as well as the limited nature of extradition hearings.

Human rights groups have repeatedly cited the alleged use of torture, arbitrary detentions, forced confessions and problems lawyers in China.

However, Hong Kong officials have defended the plans, even as they raised the threshold of extraditable offences to crimes carrying penalties of seven years or more. They say the laws carry adequate safeguards, including the protection of independent local judges who will hear cases before they are approval by the Hong Kong chief executive. No one would be extradited if they face political or religious persecution or torture, or the death penalty, they say.

The opposition to the bill has united a broad range of the community, from usually pro-establishment business people and lawyers to students, pro-democracy figures and religious groups.

“We continue to listen to a wide cross-section of views and opinions and remain to open to suggestions on ways to improve the new regime,” a Government official said on Sunday.