A sea of democracy activists flooded the streets of Hong Kong Sunday under torrential rains in a peaceful demonstration to city leaders that their movement still draws wide public support, despite mounting violence and increasingly stark warnings from Beijing.

Hundreds of thousands of umbrella-carrying protesters poured across the heart of Hong Kong island, defying both the downpour and a police order not to march from a park where they had gathered earlier for a rally.

Weeks of demonstrations have plunged the financial hub into crisis, with images of masked, black-clad protesters engulfed by tear gas during street battles against riot police stunning a city once renowned for its stability.

Sunday's action, billed as a return to the peaceful origins of the leaderless protest movement, drew more than 1.7 million people, making it one of the largest rallies since the protests began about three months ago, according to organisers the Civil Human Rights Front.

It ended a weekend of protests that, as of early Monday, saw no major confrontations with police for the first time in weeks.

"It's been a long day and we're very tired, but to see so many people out in the rain marching for Hong Kong gives strength to everyone," said Danny Tam, a 28-year-old graphic designer.

Police said only that the approved rally in the park reached an estimated 128,000 people, not including those packed into the many surrounding streets.

The unprecedented political crisis was sparked by widespread opposition to a plan for allowing extraditions to the Chinese mainland.

But protests have since morphed into a broader call for democratic rights in the semi-autonomous city.

Anger has been sharpened among protesters by the perceived heavy-handedness of the police, who have used tear gas, baton charges and rubber bullets in incidents that have gained wide attention on social media.

"The police are doing things that are totally unacceptable," said Yim, a protester who like many others gave only one name.

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"They are hurting citizens. They aren't protecting us."

Communist Party-ruled mainland China has sharpened its tone towards the protesters, decrying the "terrorist-like" actions of a violent minority.

Spiralling unrest, which last week saw protesters paralyse the city's airport, tarnished a campaign that took pride in its peaceful intent and unpredictability -- which demonstrators have tagged with the slogan "Be Water".

- Police under pressure -

Many among Sunday's rally-goers carried rucksacks stuffed with protest paraphernalia -- laser pens, gas masks, goggles and helmets.

"We have our gear with us, but we hope not to use it," said a 30-year-old identifying himself only as Man.

Late in the evening hundreds of masked protesters briefly gathered outside the government headquarters shouting "Reclaim Hong Kong, revolution of our times" before dispersing.

State media has run images of military personnel and armoured personnel carriers across the border in Shenzhen, prompting the United States to warn Beijing against sending in troops.

Analysts say any intervention by Chinese security forces would be a disaster for China's reputation and economy.

But Hong Kong's police are under intense pressure, stretched by repeated flash-mob protests.

"Only when there were violent acts or illegal behaviours which endangered the safety of people at (the) scene, police would stop them by proportionate use of force," the police said early Monday in a statement, adding that it was "unfair" to criticise the officers under such circumstances.

Opinions among the protesters have diverged over the billowing violence, which has seen a small hardcore group using rocks, Molotov cocktails and slingshots against the police.

Some say the violence has driven the pro-democracy movement in an uncomfortable direction.

"There are some expressing extreme views," rally-goer Ray Cheng, 30, told AFP.

"But we have tried many times with peaceful approaches... I really hope the government can listen to us."

- Demands unmet -

Under a deal signed with Britain, authoritarian China agreed to allow Hong Kong to keep its unique freedoms when the former British crown colony was handed back in 1997.

But many Hong Kongers feel those freedoms are being chipped away, especially since China's hardline president Xi Jinping came to power.

Beyond suspending the extradition bill, Beijing and city leader Carrie Lam have shown no desire to meet demands such as an inquiry into police violence, the complete withdrawal of the bill and an amnesty.

Beijing has pressured Hong Kong businesses to toe the line and condemn the protesters.

On Friday, Cathay Pacific Airways announced the shock resignation of CEO Rupert Hogg after the carrier was excoriated by Beijing because some staff supported the pro-democracy protests.

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