The protesters were among a group of 50 to 60 activists who kicked off a week of disruption in Sydney with an illegal march through the city centre on Monday.

Blockade Australia began its threatened protests “to cause disruption to the political and economic systems of Australia which are driving climate destruction”, with a group converging about 8am at Hyde Park.

They marched towards the harbour, chanting, playing drums, pulling down signs, dragging wheelie bins onto the road and blocking intersections.

They were met with a large police presence, including officers on horses and in helicopters.

Protesters dispersed when police stopped them at the intersection of George and Bridge streets, blocking access to the Harbour Bridge.

Blockade Australia live-streamed video of a 22-year-old woman who parked a car at the northern entrance to the Harbour Tunnel to cause more disruption.

The tunnel was shut down about 8.15 when she blocked all city-bound lanes for about an hour.

All traffic was diverted via the Harbour Bridge and traffic was backed up for several kilometres.

NSW Police say she put a bicycle lock around her neck and attached herself to the steering wheel before being removed from the car and arrested.

The group said the woman was from Lismore, the epicentre of unprecedented floods this year in northern NSW.

Police are out in force in the CBD and have a heavy presence on the Harbour Bridge after the group last week flagged a resurgence in their activities, which previously shut down Port Botany, the Harbour Bridge and the Spit bridge.

Blockade Australia said it would continue to cause disruptions all week.

“Disruption to the infrastructure of Australia’s project of exploitation is essential in cutting through the climate denial that this system survives off,” it said.

Olivia, a spokeswoman for the group, said Sydney had been where Australia’s destruction of the continent had been most intense.

“Our collective survival rests on organised opposition and the use of strategic direct action to stand against this project of destruction.”

Earlier this year, the NSW government passed legislation to crackdown on illegal protesters following several arrests of climate change activists blocking traffic and access to ports.

Protesters face a maximum penalty of two years’ jail and $22,000 fines for disrupting traffic or preventing access on roads.

The legislation also created new offences targeting people blocking access to major facilities such as ports and railways.

-AAP