About 150,000 students, parents and activists have taken to the streets to protest over the federal government's inaction on climate change.
Strikes were held across the country on Friday at 60 locations, as part of a global effort to shine a light on climate change.
The protests were estimated to be 10 times the size of those held in November.
The students have three demands: stop the Adani coal mine in central Queensland, no new coal or gas, and 100 per cent renewables by 2030.
More strikes will be planned if the students don't see the action they want from the government.
"If the politicians are just going to throw our futures away there's nothing we can do but be out here and say: we're not going to let you do that," 15-year-old Olivia Boddington told AAP at a climate strike in Canberra.
"We're not going to just go away."
Huge crowds gathered across the country on Friday, including at Sydney's Town Hall Square, outside Melbourne's Old Treasury Building and in Brisbane's CBD.
The movement was inspired by Swedish teen Greta Thunberg, who has been striking for climate action since last August.
The 16-year-old's activism has earned her a Nobel Peace Prize nomination.
Senior cabinet minister Christopher Pyne criticised the students for striking, saying the move will damage their education.
However, Labor national president Wayne Swan defended student activism.