Hundreds of thousands of schoolchildren across the world have gone on strike in protest at the escalating climate crisis.

Students from 1,800 towns and cities in more than 110 countries stretching from India to Australia and the UK to South Africa, walked out of lessons on Friday, the organisers of the action said.

This is the latest school climate strike, inspired by teenager Greta Thunberg, who has become a global figurehead since protesting outside Sweden’s parliament in 2018. The young people are demanding politicians take urgent action to avoid catastrophic ecological breakdown.

In London, thousands gathered in the sunshine in Parliament Square chanting, “Where the fuck is the government”, and “This is what democracy looks like”, before staging a sit-down protest outside the department of education.

Ivy, 14, from Surrey, said: “I am here because I believe there is no point having an education if there is no future … I am so frustrated the only people who really care about this are the ones who can’t vote.”

Her friend, Arissa, added: “It is not us that did this – we are only 14 – but no one else is doing anything about it and it’s our future, so what choice do we have?”

There were similar demonstrations in cities across the UK with organisers reporting record numbers in several places.

In Glasgow, Nancy Baijonauth, 16, declared the protest the biggest so far in the city. “It’s really great. It felt like at the start people were hesitant, maybe because they felt nervous and that they couldn’t make a change, but now more people are joining in.”

In Cambridge about 2,000 school students demonstrated and there were big protests in cities from Leeds to Bristol, Manchester to Cardiff.

Globally, organisers said that hundreds of protests also took place in the US.

The school protests come amid growing evidence of the scale of the climate crisis. Last year, the UN’s leading scientists warned that there were just 12 years to limit climate catastrophe. Earlier this month, another UN report warned that the widespread collapse of ecosystems was putting humanity itself at risk. And just last week it emerged that the Antarctic ice is melting much faster than previously feared and global atmospheric CO2 emissions reached a record level of 415ppm.

The school strike movement started last August whenThunberg, then 15, held her solo protest in Stockholm. Since then it has snowballed to be one of the most significant climate movements in history.

On Friday Thunberg, and leading youth strikers across the world, called for all adults to join the protests and stage a global general strike on 20 September.

Writing in the Guardian they said: “We’re asking adults to step up alongside us … today, so many of our parents are busy discussing whether our grades are good, or a new diet or the Game of Thrones finale – whilst the planet burns,” they write. “But to change everything, we need everyone. It is time for all of us to unleash mass resistance … if we [demand change] in numbers we have a chance.”

Before Friday’s strikes, organisers said the number of young people taking part would top the 1.4 million people who participated in the last global day of strikes in March.