The protests, which carry the social media hashtag #LetThemStay, come after yesterday's High Court ruling that 267 people, including 37 babies and 54 children, would be transported back into detention in Nauru.
A protest infront of Sydney's Department of Immigration building today attracted hundreds, with constant chants of 'Let them stay'.
Tweets from people at the rally.
Protests in Melbourne, Canberra and Newcastle are scheduled today at 5.30pm, and Perth at 6.30pm.
Protests in Brisbane, Adelaide and Hobart will follow on Friday and in Darwin on Monday.
On Thursday morning several Anglican churches around Australia announced they would offer sanctuary to asylum-seekers in danger of being sent back to Nauru.
The UN refugee agency has warned Australia must consider the best interests of children following the High Court ruling.
Sydney paediatrician Hasantha Gunasekera, who has visited Nauru, told SBS the High Court decision was "disappointing".
"Health professionals with experience in the detention network are consistent in our calls to remove children from this environment," he said.
"The children, some who have spent most of their lives locked up behind fences, deserve better."
Under the government’s Border Force Act, doctors are restricted in what they can say about what they witness inside immigration detention centres.
But Dr Gunasekera said he felt compelled to speak out despite the risks.
"I felt I had no choice but to let the Australian people know what we are doing to already-traumatised kids," he said.
A poster made to promote the protests. Source: Twitter
Twitter has been red hot with #LetThemStay hashtags.
