NSW Police told AAP officers arrived at the park in Tempe on Wednesday after receiving intelligence members of the group had been gathering there.
One woman was arrested nearby Turella Reserve, however it remains unclear if she was connected to the group, a police spokeswoman said.Â
Zelda Grimshaw, a communications professional linked to Blockade Australia, said police had raided a peaceful picnic attended by 30 members of the activist group.
"Police came ... with helicopters, unmarked cars, plainclothes officers, and pulled people off pushbikes and threw people to the ground and detained and searched people who were peacefully having a picnic in a park," Ms Grimshaw said.
One person was arrested for having graffiti implements after police discovered felt tip pens, and another had been asked to leave NSW after police found gardening implements in their car, she said.
"We feel like we're in a car driving at rapid speed towards the cliff, and what we're being asked to do is to protest, you know, nicely," Ms Grimshaw said.
Ms Grimshaw said she hoped further protests would go ahead on Thursday and Friday but could not say what was planned.
Organisers said Wednesday would be a day of rest for the activist group, after two days of marches and demonstrations in the CBD resulted in 21 arrests.
"We have made the call for tomorrow to be a day off," they said on the Telegram messaging platform via the Blockade Australia: Resist Climate Inaction channel.
"We want people to have a chance to rest, regroup and support one another as well as connect with those who share our common purpose of resisting climate destruction."
NSW Premier Dominic Perrottet has called the activists "bloody idiots", saying their actions did not aid their cause.
Protesters who disrupt major roadways, ports and railways can now be charged with newly-legislated penalties of up to two years in prison and a fine of $22,000.
A total of 32 people have been arrested since NSW Police set up Strike Force Guard in March to prevent, investigate and disrupt unauthorised protests.
