More than 1,000 people rallied in central Sydney in support of Hong Kong protesters on Sunday, kicking off a day of planned "anti-totalitarianism" demonstrations globally.

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

Some 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 major cities across the country on Sunday.

Pro-China supporters stayed away, avoiding a repeat of the tense scenes that flared last month when opposing rallies held on the same day led to confrontations between the two sides.

Bill Lam, 25, who attended demonstrations in Hong Kong before moving to Sydney for study two months ago, said protesters had become "very desperate" and simply wanted authorities to respect "their basic human rights".

"I came here but I want to support them from Australia," he told AFP.

"I feel so sad every night because I watch the live video (from Hong Kong) on Facebook and some social media."

Frankie Lo, 47, said he had lived in Australia for years, but continued to care deeply about the situation back home.

"We still believe in one country, two systems but they just have to follow the basic law. It's not about independence," he said, adding that besieged Hong Kong chief executive Carrie Lam should set up an independent committee to investigate allegations of police brutality.

"It's something that we don't want to see," 25-year-old Tony Chung said of the violence that has featured in many of the protests in the city.

"It's Hong Kong people fighting against Hong Kong people, which doesn't make sense at all."

Similar rallies are being held in more than 40 cities worldwide as part of a global day of action in support of Hong Kong protests.