Hundreds of thousands of people dressed in black have taken to the streets in Hong Kong to demand the city's embattled leader steps down, a day after she suspended an extradition bill in a dramatic retreat following the most violent protests in decades.

Protest organisers are hoping more than a million people turn up for Sunday's rally, a similar number they estimated for a demonstration against the proposed extradition bill last Sunday.

Police put that count at 240,000.

Carrie Lam faces the fight of her political life. ( AP: Kin Cheung )

Activists set up gazebos as protesters, some carrying flowers, started to gather in sweltering summer heat to march from Victoria Park to Hong Kong's central government offices.

Beijing-backed Hong Kong Chief Executive Carrie Lam on Saturday indefinitely delayed the extradition bill that could send people to mainland China to face trial, expressing "deep sorrow and regret".

The about-face was one of the most significant political turnarounds by the Hong Kong government since Britain returned the territory to China in 1997, and it threw into question Ms Lam's ability to continue to lead the city.

Pressure was mounting on Ms Lam after the mass demonstrations.

"Her government cannot be an effective government, and will have much, much, much difficulties to carry on," veteran Democratic Party legislator James To told government-funded broadcaster RTHK.

"I believe the central people's government will accept her resignation."

Young and old braved the Hong Kong summer heat to protest the extradition law yet again. ( ABC: Nick Dole )

Activist investor David Webb, in a newsletter on Sunday, said if Ms Lam was a stock he would recommend shorting her with a target price of zero.

"Call it the Carrie trade. She has irrevocably lost the public's trust," Mr Webb said.

"Her minders in Beijing, while expressing public support for now, have clearly lined her up for the chop by distancing themselves from the proposal in recent days."

More protests have been promised, despite the Government suspending the passage of its controversial extradition bill. ( ABC News: Nick Dole )

Violent clashes on Wednesday, when police fired rubber bullets and tear gas at protesters near the heart of the financial centre, grabbed global headlines and forced some banks to shut branches.

Some Hong Kong tycoons have started moving personal wealth offshore over concerns about the proposed extradition law, which critics warn could erode the city's international status.

After daybreak on Monday, police announced that they wanted to clear the streets of protesters and lined up several officers deep and to face off against several hundred demonstrators on a street in central Hong Kong.

The police asked for cooperation in clearing the road. Protesters replied with chants, some kneeling in front of the officers.

Beijing accused of extensive meddling in Hong Kong

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 23 seconds 23 s A timelapse of the Hong Kong march shows protesters flooding the streets.

The city's independent legal system was guaranteed under laws governing Hong Kong's return from British to Chinese rule 22 years ago, and is seen by business and diplomatic communities as its strong remaining asset amid encroachments from Beijing.

Hong Kong has been governed under a "one country, two systems" formula since its return to Beijing, allowing freedoms not enjoyed on mainland China but not a fully democratic vote.

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Many accuse Beijing of extensive meddling since then, including obstruction of democratic reforms, interference with elections and of being behind the disappearance of five Hong Kong-based booksellers, starting in 2015, who specialised in works critical of Chinese leaders.

Some opponents of the extradition bill said a suspension was not enough, arguing it should be scrapped and Ms Lam should go.

"If she refuses to scrap this controversial bill altogether, it would mean we wouldn't retreat. She stays on, we stay on," said pro-democracy politician Claudia Mo.

Asked repeatedly on Saturday if she would step down, Ms Lam avoided answering directly and appealed to the public to "give us another chance".

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 50 seconds 50 s Hong Kong Chief Executive says she would never 'sell out' the city

Ms Lam said she had been a civil servant for decades and still had work she wanted to do.

She added she felt "deep sorrow and regret that the deficiencies in our work and various other factors have stirred up substantial controversies and disputes in society".

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Meanwhile, Ms Lam's reversal on the bill was hailed by business groups and overseas governments.

The UK Foreign Secretary Jeremy Hunt said on Twitter: "Well done HK Government for heeding concerns of the brave citizens who have stood up for their human rights."

"AmCham is relieved by the government decision to suspend the extradition bill and that it listened to the Hong Kong people and international business community," Tara Joseph, president of the American Chamber of Commerce in Hong Kong, said.

The Hong Kong protests have been the largest since rallies after the Tiananmen Square massacre. ( ABC: Nick Dole )

Fear of forced confessions, arbitrary detention

China's top newspaper on Sunday condemned "anti-China lackeys" of foreign forces in Hong Kong.

"Certain people in Hong Kong have been relying on foreigners or relying on young people to build themselves up, serving as the pawns and lackeys of foreign anti-China forces," the ruling Communist Party's official People's Daily said in a commentary.

A man pays his respects at the site where a man fell to his death while hanging a protest banner in Hong Kong. ( AP: Vincent Yu )

"This is resolutely opposed by the whole of the Chinese people including the vast majority of Hong Kong compatriots."

The Hong Kong protests have been the largest in the city since crowds came out against the bloody suppression of pro-democracy demonstrations centred around Beijing's Tiananmen Square on June 4, 1989.

Organisers hope more than a million people will join today's demonstration. ( Reuters: Tyrone Siu )

Officials said 72 people were admitted to hospitals during Wednesday protest, while a man died on Saturday after plunging from construction scaffolding where he unfurled a banner denouncing Hong Kong's extradition bill, local media reported.

Ms Lam had said the extradition law was necessary to prevent criminals using Hong Kong as a place to hide and that human rights would be protected by the city's court which would decide on the extraditions on a case-by-case basis.

Critics, including leading lawyers and rights groups, note China's justice system is controlled by the Communist Party, and say it is marked by torture and forced confessions, arbitrary detention and poor access to lawyers.

Opponents of the extradition bill say suspension is not enough and want it scrapped. ( AP: Kin Cheung )

Reuters