The unsolicited mural showed a sleeping Mother Earth nestled against an Illawarra escarpment-esque landscape.

Was Mother's sound slumber the result of a recent COVID-19-linked drop in carbon emissions? Was she happy?

Climate emergency collective Extinction Rebellion (XR) Northern Illawarra set out to invite these questions and more, after rallying a group of artists to complete the work Thursday night.

"We are trying to push out a message about climate change and the importance that we act on that," said the collective's Ben Lofthouse. "Using street art or interactive murals is the perfect way to engage people."

At the weekend, passers-by used chalk to colour in parts of the mural or add their own message about climate change.

"We had lots of kids there, colouring in and asking questions," said the collective's Laura Scalafiotti. "It's a really beautiful artwork that has brought people together."

But despite a largely warm reaction on social media - and at least one man who rang council to urge otherwise - the work was painted over by council staffers on Monday in line with the city's strict no-graffiti policy.

"Over the weekend a section of the heritage precinct around Thirroul Pool was graffitied," a council spokeswoman said. "The graffiti is extensive and covers four panels of the Thirroul Pool wall along the promenade."

"This graffiti was not requested or approved by Council. In addition, Council currently has no plans for public art at this location.

"While we appreciate some might view this graffiti as more creative and artistic than a tagging incident, this is graffiti and it's not the location for such imagery."

The northern Illawarra arm of XR formed late last year, mobilising acts including a flash mob at Coledale Christmas market and a "guerilla tree-planting protest" in Thirroul in March.

Member Amy Luschwitz said the collective included about 200 people, many of them parents motivated to action by their children.

"There are some poeple who don't really see [the mural] it as an act of civil disobedience; they see it more as a community project that is going to start debate," she said.

"I hope that wollongong council wasn't too upset, given that its citizens generally care about climate change and have prioritised that. I think it should be really proud of people showing the initiative."

Ms Luschwitz said it never mattered whether the mural lasted.

"It sparked something in peoples' consciousness, to think about the land as our mother, who we should all be caring for."