Australia's Victoria State has reported a jump in new Covid-19 infections as Melbourne braces for a third straight day of protests against lockdown restrictions, with police deploying in strength to disperse crowds.

Protesters began gathering in the city centre in separate groups as the state's Police Chief Commissioner Shane Patton vowed to prevent more violent protests but declined to discuss the measures planned to control violence or unruly behaviour.

"I'm not going to talk about the tactics we'll deploy today," Patton said at a media briefing in Melbourne, the state capital. "I want them to be completely unaware of what we're going to do and what capacity they may face."

Television footage showed crowds of protesters walking in the middle of streets in different parts of the city, with police sometimes giving chase.

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