The Global Strike 4 Climate took place in 110 towns and cities across Australia on Friday, with organisers demanding a target of net zero carbon emissions by 2030 and a transition to 100 per cent renewable energy.

Millions of people around the world on Friday also took to the streets, including 16-year-old Swedish climate activist and strike organiser Greta Thunberg, who participated in demonstrations in New York City.

She will take part in the United Nations' youth climate forum on Saturday and address world leaders at the UN secretary-general's climate summit on September 23. Prime Minister Scott Morrison will not attend the summit.

Australians, of all age groups, backed her call for a climate strike on Friday, September 20.

Teachers, union members, grandparents, heavily-pregnant women and a man in a dinosaur suit holding a sign saying "Extinction sucks, trust me" showed up at Australian rallies to support the student-led protest.

Organisers say more than 300,000 people attended the protests across the country, double the turnout of the most recent national protest in March.

The worldwide strike movement began in August 2018 when Thunberg began protesting outside Sweden's parliament on school days.

She tweeted support from New York for the students gathering in Australia, saying they were "setting the standard" for other countries.