Thousands of protesters have gathered in central Melbourne and Sydney to call for more action on climate change and the sacking of Prime Minister Scott Morrison amid the country's bushfires crisis.

Despite pleas from Victorian police and the premier to reschedule the Melbourne event to a less risky fire day, several thousand protesters huddled under umbrellas at the State Library.

Many held banners which read "Time is Running Out," "Declare a Climate Emergency," "You have blood on your hands, Morrison," "Make Fossil Fuels History," and "Sack ScoMo."

Thousands rally at Sydney Town Hall amid the ongoing bushfire crisis. (Getty)

Many of the signs featured burning koalas. (9News)

More than 10,000 people rallied at Town Hall Square in Sydney with similar banners.

Protesters in both cities chanted "ScoMo has got to go" while Sydney protesters also yelled "the liar from the shire our country is on fire."

Sydney protester Ambrose Hayes, 14, told AAP people were "fed up" with Mr Morrison because he's not acting enough on the "climate crisis".

"This (the bushfire crisis) is caused by climate change, there is no denying it and they're (the government) just letting it happen," he said.

"They're not listening to us."

A woman and child attend rallies. (Bryce Waters)

Activists rally for climate action at Sydney Town Hall. (Getty)

Izzy Raj-Seppings, the 13-year-old who made headlines when she was moved on by police during a climate protest outside Kirribilli House in December, called on Mr Morrison to step up.

"What have you done when your country burns? What have you done when the kids are crying?," she said on Friday.

Hundreds of protesters also rallied in Adelaide and Brisbane.

Mr Morrison this week announced an initial $2 billion bushfires recovery fund and handed over an immediate payment of $60 million to council areas affected by the fires.

He has flagged a royal commission and says any national inquiry into the bushfires crisis would need to examine the impact of climate change.

A couple embraces as they take part in climate change protests. (Bryce Waters)

A man speaks through a megaphone as thousands take part in protests in Melbourne and Sydney. (Bryce Waters)

But while acknowledging there was an appetite to examine the impacts of climate change, he said he would not consider a stronger commitment to carbon emission reductions.

Australia was already "meeting and carrying" its burden on greenhouse gas emissions, Mr Morrison said on Friday.

The Melbourne protest was criticised by Premier Daniel Andrews who warned the protesters could jeopardise their standing by staging a protest that diverts police resources away from bushfires.

"The protest, against the advice of the police, in the middle of a disaster, that is when you start losing public support, not adding to your public support," he told reporters on Friday.

"I respect people's right to have a view, I tend to agree with a lot of the points that are being made - climate change is real - but there is a time and a place for everything and I just don't think a protest tonight was the appropriate thing to do."

The organisers are expecting as many as 20,000 people. (9News)

A popular chant in Sydney was "Scomo's gotta go". (9News)

Fury over Melbourne rally

Victorian Premier Daniel Andrews sent organisers of the protest a stern warning on Thursday, telling ABC Radio "they risk losing support from those like him that believe in climate change".

"I don't disagree with them on a range of different points they'd make," the premier told 3AW on Thursday.

"But I tell you what, you lose me and you lose a lot of other fair-minded Victorians who believe in climate change when you have a protest, when you've been told point-blank you are diverting police resources."

The warnings were previously voiced by Emergency Services Minister Lisa Neville, who on Wednesday said she was stunned to hear the protests were going ahead.

One sign read "Make the earth cool again". (9News)

"This is a really reckless and selfish thing people are doing. There is a time for protests. It's not this Friday," she said.