* HK experiencing most serious revolution since 1997 -Jasper Tsang
* Organisers say 316,000 attend rally, police estimate 103,000
* Security tight ahead of mass protest planned for Sunday (Adds quote and rally numbers in paragraphs 4, 11)
By Alun John and Vimvam Tong
HONG KONG, July 20 (Reuters) - Tens of thousands gathered in Hong Kong on Saturday to voice support for the police and call for an end to violence, after a wave of protests against an extradition bill triggered clashes between police and activists and plunged the city into crisis.
The rally, called "Safeguard Hong Kong", comes a day ahead of another mass protest planned against the government and its handling of the now-suspended extradition bill that would have allowed people in Hong Kong to be sent to mainland China for trial.
Police have called for calm ahead of Sunday's protest, where security is expected to be tight. Authorities have removed metal barriers - which activists have used to block roads during previous demonstrations - from areas around the march route.
"We are experiencing the most serious revolution after Hong Kong's handover," said former Legislative Council president, Jasper Tsang. "We are also experiencing the most serious challenge for "One Country, Two Systems," he added, referring to the system under which Hong Kong is governed since its handover from British to Chinese rule in 1997.
Hong Kong's embattled leader, Carrie Lam, has apologised for the turmoil the extradition bill has caused and declared it "dead", although opponents say nothing short of its full withdrawal will do.
Demonstrators, mostly middle-aged or older and dressed in white, braved heavy rain and thunderstorms to gather at the city's Tamar Park, next to the Legislative Council which protesters stormed and raided on July 1 - the 22nd anniversary of Hong Kong's handover from British to Chinese rule.
Some waved Chinese flags as others chanted "Hong Kong Cheer Up" and "Support Hong Kong Police".
A fleet of around 12 fishing boats circled Victoria Harbour next to the rally with banners draped over the side of the vessels that read "Put away the combat, fight for Hong Kong" and "Cherish Hong Kong, we're all in the same boat".
"Violence is intolerant. We are distressed about our home and we should absolutely stand out to support Hong Kong police, to maintain stability and rule of law in society," said Tsol Pui, 85, president of Hong Kong Veterans' Home.
Echoing that sentiment, Tang King Shing, Hong Kong's former Commissioner of Police, said: "Police, we support you. You should not have suffered from the disaster made by those thugs... We Hong Kong people come out to safeguard Hong Kong."
Organisers said 316,000 attended the rally. Police put the number at 103,000 at the peak.
Last weekend two initially peaceful protests degenerated into running skirmishes between baton-wielding riot police and activists, resulting in scores of injuries and more than 40 arrests.
Those fights followed larger outbreaks of violence in central Hong Kong last month, when police forced back activists with tear gas, rubber bullets and bean-bag rounds.
Activists and human rights groups have called for an independent investigation into what they describe as excessive use of force by police.
The protesters are also demanding the word "riot" be withdrawn from the government's description of demonstrations and the unconditional release of those arrested.
What started as protests over the extradition bill have now morphed into demands for greater democracy, the resignation of leader Lam, and even curbing the number of mainland Chinese tourists to Hong Kong.
Under the terms of the handover from Britain in 1997, Hong Kong was allowed to retain extensive freedoms not enjoyed on the mainland under a "one country, two systems" formula, including an independent judiciary and right to protest.
But for many Hong Kong residents, the extradition bill is the latest step in a relentless march toward mainland control.
Other anti-government protests are planned over coming weekends in areas including Mong Kok, a gritty working-class district across the harbour from the financial centre, and in Tseung Kwan O and Sham Shui Po, one of the city's poorest areas.
Opponents of the extradition bill fear it would leave Hong Kong people at the mercy of Chinese courts, where human rights are not guaranteed, and have voiced concerns over the city's much-cherished rule of law. (Additional reporting By Kevin Liu and Felix Tam, Writing by Anne Marie Roantree; Editing by Gareth Jones and Stephen Powell)
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