The Melbourne events are part of worldwide protests organised by activist group Extinction Rebellion.
Jane Morton, a semi-retired clinical psychologist and rebellion volunteer, said she would be “prepared to die” if it meant action would be taken on climate change.
She said protesting was “like a war” and “unprecedented action against climate change” was needed.
“We are risking passing the point of no return for a hot house earth, which is an uninhabitable earth,” she said.
Ms Morton said the protests were about “sounding the alarm” for the “future of the whole human race”.
Activists will converge on the corner of Bourke and Russell streets about 5pm on Monday before marching to other “secret” CBD locations, with plans to block traffic.
Yarra Trams has advised route 86 and 96 trams will divert via La Trobe Street between Spencer Street and Melbourne Museum, with commuters encouraged to consider alternative routes.
Ms Morton apologised for the disruption, but said “somehow we have to get the ear of government”.
On Monday morning, about 30 protesters were perched on the steps at Parliament House to meditate, with organiser Kathryn Joy saying it was a “peaceful way to to take action”.
The meditation will run until sunset.
There is a strong police presence throughout the CBD and in Carlton Gardens.
Protesters say the Spring Rebellion will be non-violent but highly disruptive.
Melbourne grandmother Carol Ride was among the crowd at Carlton Gardens on Monday, and said she was there because she cared “about the future for my children and grandchildren”.
She said people were feeling “deep grief and despair” about climate change.
“People need to be taken seriously,” Ms Ride said.
She said the Extinction Rebellion movement provided a place for people to express their feelings and fears about the future.
Melbourne activists are planning daily road blockades, a nude march and a disruptive bike ride.
On Thursday – the day tram drivers strike from 10am to 2pm – there will be three protests in the city at RMIT in Swanston Street, Alexandra Gardens and at Batman Park.
Locations of other strikes remain undisclosed for maximum disruption.
Police said general duties police would be backed by the Public Order Response Team, the Mounted Branch and the Transit Safety Division.
Commander Tim Hansen said a heavy police presence aimed to ensure there were no breaches of the peace or other offences.
“Everyone has a right to protest peacefully without impacting the rest of the community, who also have the right to go about their daily business,” he said.
Yarra Trams is urging city commuters to prepare for longer travel times.
“Tram passengers travelling in the CBD or Carlton area this week should allow extra time and check the PTV website or smartphone app to get the latest travel advice,” the spokesperson said.
Motorists should visit traffic.vicroads.vic.gov.au or download the VicTraffic app for the latest traffic information.
Carolyn Webb is a reporter for The Age.