London (AFP) - Thousands of schoolchildren went on "strike" across Britain on Friday in a protest against climate change, with hundreds rallying in London's Parliament Square.

Children of all ages chanted "save our planet", cheered as flares were lit and clambered onto statues in the shadow of Big Ben to call for action, and to raise awareness.

"As humans, we got ourselves into this predicament, it's our responsiblity to get out of it," said Hal, a 15-year-old from London.

"As well as being a message to the politicians, it's a way to spread awareness to everyone," added the teenager, who was wearing his school uniform "to accentuate the fact that I should be at school".

The protesters waved makeshift placards reading "Make Earth Cool Again", "Don't Mess With My Mother", "We Stand For What We Stand On" and "I'm Getting Detention For This".

There were similar protests in dozens of British towns and cities, including Brighton, Leeds, Manchester and Oxford.

Many of the children said their schools had shown them leniency in attending the "Youth Strike 4 Climate" event, part of a Europe-wide movement that has seen walkouts in Belgium, France, Germany, and Sweden.

Young protesters have been gathering in Brussels and other Belgian cities on Thursdays for around six weeks, with approximately 11,000 turning out in the capital this week.

Demonstrators also took to the streets of European cities like Paris, Potsdam and Munich on Friday, according to organisers.

"I'm originally from Germany so my friends already did it, then I saw people talk about it, and I said 'Oh my god, I've got to come," art student Emily El-Harake, 17, told AFP in London.

The teenager called on politicians to get Brexit sorted quickly in order to focus on "more important issues" like the environment.

"Young people are a lot more conscious of it, most people I know, we buy our clothes second hand," added friend Erin Mantle, 16, who said their school was supportive of their strike.

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"It's the little things that we are doing but it's the government that needs to do the big things."

- 'Stop being selfish' -

Prime Minister Theresa May's office said it was good that young people were "engaged in the issues that affect them", but that the protest "wastes lesson time that teachers have carefully prepared for."

The movement was inspired by the actions of Greta Thunberg, a 16-year-old girl who held a solitary protest outside the Swedish Parliament in Stockholm last year.

She responded Friday to Downing Street's criticism of the demonstrations.

"Political leaders have wasted 30 (years) of inaction. And that is slightly worse," she wrote on Twitter.

Geography student Paige Reardon, 16, said her teacher was "happy that I was going" to the protest, and urged politicians to take action.

"They need to consider it's their children and grand children who are going to suffer. Stop being selfish."

Some parents were also in attendance, including Minnesota native Sally Hodgkinson, 42, and her 11-year-old daughter Isis.

"She expressed an interest, as did some kids from her school, and I thought it was a good way for them to get engaged," said mother Sally.

"It has to be put to the top of the agenda."

Student Hal said that social media was helping young people to coordinate action worldwide.

"It would've been a much smaller cause without it. It's a really good thing social media brought all these people together."