Tens of thousands of young Australians have walked out of their classrooms to stage protests in capital cities demanding action on climate change.

Key points: Students have used a combination of humour, passion and urgency in protests across the country

Students have used a combination of humour, passion and urgency in protests across the country The protests were inspired by the actions of a 16-year-old Swedish student, Greta Thunberg, in Stockholm

The protests were inspired by the actions of a 16-year-old Swedish student, Greta Thunberg, in Stockholm PM Scott Morrison objected to a previous similar protest, saying he didn't want to see "schools being turned into parliaments"

Rallies began in Melbourne, Sydney, Adelaide, Canberra and Hobart outside state parliament buildings and town halls on Friday.

Students have also marched at rallies across regional Australia, with large crowds protesting at Geelong, Byron Bay, Coffs Harbour, Cairns and Townsville.

Many used humour to get their point across, with posters referencing internet memes and suggesting fail grades for the nation's political efforts on climate change policy.

Others were more serious — one poster urged politicians to "panic" about addressing climate change and another warned "there is no Planet B".

Melbourne protest organisers said about 20,000 people attended the rally outside Parliament House. ( ABC News: Stephanie Anderson )

In Melbourne, protesters filled Spring Street in the CBD, blocking traffic and trams and chanting "this is what democracy looks like" and "students united will never be divided".

Milou Albrecht and Harriet O'Shea Carre, both 14, travelled from Castlemaine in central Victoria to march in Melbourne.

Harriet O'Shea Carre and Milou Albrecht travelled with 400 of their fellow students to make the Melbourne march. ( ABC News )

The pair started the rally last year and were joined by 400 others from Castlemaine Secondary School.

"Together our collective voice is very strong and powerful," Harriet said.

What do the students want? Stop the Adani coal mine in central Queensland

Stop the Adani coal mine in central Queensland No new coal or gas projects

No new coal or gas projects 100 per cent renewables by 2030

Hobart College student Imogen Viner said she was concerned about the future of forests in Tasmania.

"Specifically for Tassie, we want to look at stopping how much forestry she's got going on," she said.

Frida Elliott, 15, said she did not care whether her school supported her presence at the Hobart rally.

"We're told we shouldn't be missing class time by our teachers … but there's nothing they can do about it and they've taken a step back and realised the power we have here," she said.

Rallies were also held in Darwin, Brisbane and Perth.

Hundreds of students defied school warnings to attend a rally at Peregian Beach on the Sunshine Coast. ( ABC News: Megan Kinninment )

There were 50 rallies planned across the country for students to protest against what they see as the destruction of their future.

Meanwhile, New Zealand rallies have seen strong turnouts, with a student march blocking streets in Wellington this morning.

Thousands of protesters gathered in Perth's CBD to join the nationwide movement. ( ABC News: Evan Morgan Grahame )

Students 'on the right side of history'

The protests were inspired by 16-year-old Swedish student Greta Thunberg, who pledged to protest outside the Parliament in Stockholm until the country caught up on its commitments under the Paris Agreement.

Greta urged students to ignore calls from some politicians to stay in school.

Students in Byron Bay ditched school to join the global movement. ( ABC News: Sam Turnbull )

"I say that the children are on the right side of history and that those politicians are not," she said.

"So they should keep on fighting and they must be prepared to go on for a very, very long time.

"I don't think decision-makers will get the message for a very long time."

In Melbourne, students staged their protest outside Parliament House. ( ABC News: Bez Zewdie )

Federal Education Minister Dan Tehan said he would meet with the climate strikers to discuss their concerns outside of school hours, while Queensland Premier Annastacia Palaszczuk said the protests should have been held on a weekend.

"Students leaving school during school hours to protest is not something that we should encourage," Mr Tehan said.

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"Especially when they are being encouraged to do so by green political activists."

Similar protests in November prompted Prime Minister Scott Morrison to warn against the idea of students leaving school to participate in protests.

"We don't support our schools being turned into parliaments. What we want is more learning in schools and less activism in schools," Mr Morrison said at the time.

Students are calling for a switch to renewable energy. ( ABC News: Gabriella Marchant )

But other politicians have thrown their support behind the rallies.

NSW Opposition Leader Michael Daley encouraged students to exercise their "democratic right" to protest.

Independent MP Julia Banks said she was proud to support students for "using their voice".

"This is their time," she said on Twitter.

Signs got creative in Hobart. ( ABC News: Monte Bovill )

Greta received a nomination for the Nobel Peace Prize for her efforts starting a global climate change movement.

Her view is shared by students around the globe, including the 15-year-old student organiser for the Sydney school strike, Jean Hinchcliffe.

"I believe that I have learnt much more from these strikes and the organising process than I have learnt in any lesson during school," she told the ABC.

"The amount of experience you gain from it and learning to mobilise and participate in democracy I think is far more worthwhile than any history lesson."

At the November protests, students filled arcades and city squares, defying calls by the Prime Minister to stay in school, to call for an end to political inertia on climate policy.

Students gathered on the steps of South Australia's Parliament House. ( ABC News: Gabriella Marchant )

Ruby Clark, 12, was among thousands of protesters gathered at Garema Place in Canberra. ( ABC News: Niki Burnside )