Thousands rallied in Sydney and Taipei to support Hong Kong democracy protesters on Sunday, kicking off a day of planned "anti-totalitarianism" demonstrations globally.

In one of the largest solidarity marches in Australia since Hong Kong's latest pro-democracy movement began in June, black-clad participants took to the streets chanting "Add oil", a protest slogan denoting encouragement.

Some Sydney protesters held signs that read "Save Hong Kong" and "Stop tyranny", while others carried yellow umbrellas or handed out paper cranes in scenes that played out in other major cities across the country on Sunday.

"To the Chinese government and the Hong Kong government, I will use a quote from Winston Churchill from World War Two: that we shall never surrender," one protester told the crowd.

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The Sydney event came after violence flared in the Chinese-ruled city over the weekend as police and protesters clashed. Hundreds of pro-Beijing supporters also gathered in Hong Kong on Sunday.

The demonstrations kicked off in June over a now-withdrawn bill that would have allowed extraditions to mainland China.

AAP

Protesters have five demands - one of which was the bill's withdrawal - and in Sydney on Sunday, they said they would fight until all of the demands were met.

Others include an independent investigation into alleged police brutality and the release of arrested demonstrators.

"We will fight for democracy and we will fight for a government that will be responsible to the people and no one else," one protester said in Sydney.