Thirty climate activists have been arrested in Sydney at the start of a week-long mission to make a ruckus across the nation, with campaigners claiming there needs to be a "massive disruption".
The Extinction Rebellion movement has planned a "spring rebellion" running from Monday to Sunday including marches and other protests aimed at blocking traffic.
Police arrested 30 protesters in Sydney on Monday afternoon including former Greens senator Scott Ludlam and - according to organisers - four girls aged under 16.
"Our government has catastrophically failed all of us," Mr Ludlam said as he was led away by officers.
Australian writer Jeff Sparrow compared the Extinction Rebellion protests to the Greensboro anti-segregation sit-ins in the 1960s during the American civil rights movement.
Sparrow told the Sydney crowd scientists' warnings on climate change meant simultaneous "massive disruption" was needed.
"We need disruption of our transport system, we need disruption of our housing system, we need disruption of the economy to move it into a carbon-neutral phase."
Earlier in the day, Victorian activist Miriam Robinson said the group must "get right up in people's grills" to convince governments to take firm action on climate change.
"We always apologise for causing inconvenience," the retired public servant told AAP on Monday.
"But this is nothing compared to the inconvenience that is going to start happening when we start to run out of food and water."
Protesters planned to block an intersection in Melbourne's CBD on Monday evening.
In Canberra, nearly 300 people marched across Commonwealth Bridge on Monday morning, blocking traffic.
A march was also held in Brisbane where people made their way across Victoria Bridge.
In Hobart, about 30 people crossed the Tasman Bridge - although they were on a public walkway - with another handful stationing themselves outside state parliament.
In Perth, activists focused on the perspective of traditional owners with an indigenous "welcome to country" ceremony.
Authorities warned they would intervene if there was violence, significant disorder or if a safety risk was identified.
After making 30 arrests, NSW Police said the alleged offences ranged from obstructing traffic to disobeying reasonable direction.
Assistant Commissioner Mick Willing said police respected the right of groups to protest but "we have a responsibility to the community and local businesses to ensure they can go about their normal activities without being impacted on or put at risk".
Victoria Police Commander Tim Hansen stressed members of the public had a right to freedom of movement.
"Not only do you have human rights you also have human rights responsibilities here," he warned protesters on 3AW.
Extinction Rebellion specifically wants governments to "tell the truth" about climate change by declaring a climate and ecological emergency.
It also wants them to prevent biodiversity loss and reduce greenhouse gas emissions to zero by 2025 and let the public drive decisions on climate change through a citizens' assembly.
Australian Associated Press