Millions of people, mostly students and children, have taken part in demonstrations calling for urgent action from their governments to tackle climate change.
The protests, inspired by Swedish teenage activist Greta Thunberg, started in the Pacific islands and then continued across Australia, Japan and South East Asia before moving on to Europe, Africa, the Middle East and the Americas - 139 nations in all.
Young people stayed away from school while employees did not go into work during the day of mass protests.
An estimated 250,000 people gathered in New York to hear Greta, 16, tell them their efforts have put world leaders under fresh scrutiny.
She said: "The eyes of the world will be on them. They have a chance to prove that they too are united behind the science. They have a chance to take leadership to prove they actually hear us.
"Do you think they hear us?"
"No," the huge crowd replied.
To wild cheers - followed by chants of "Greta! Greta!" - she told them: "We will make them hear us."
"We will make them hear us," she told them, to wild cheers, followed by chants of "GRETA, GRETA".
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In Sydney and Canberra, demonstrators called for Australia - the world's largest exporter of coal and liquid natural gas - to do much more to reduce greenhouse gas emissions.
More than 300,000 protesters took to the streets - making it the largest demonstration in the country since the Iraq war began in 2003.
Tens of thousands of people across the UK also demonstrated - including in London, where organisers estimated 100,000 attended a rally in Westminster.
The Metropolitan Police said there had been eight arrests in London during the day's protests.
Seven people were detained under Section 14 of the Public Order Act 1986 for breaching conditions imposed on the protest while a man was arrested on Lambeth Bridge on suspicion of discharging a flare.
Sky's Laura Bundock said: "Even organisers admitted they were surprised by the size of the crowds in the capital's climate strike. Thousands and thousands filled the streets around Westminster."
One new dad said the birth of his little daughter motivated him to get involved, adding: "We have to be heard for the sake of our children. Time is running out."
More than 20,000 were thought to have marched in Edinburgh and 10,000 in Brighton.
In Belfast, organisers put the turnout at between 3,000 and 4,000, with young people taking over the Corn Market area of the city centre and staging a "mass die-in".
And in Birmingham, about 3,000 protesters, including hundreds of children, gathered in the city's Victoria Square before marching through nearby streets.
UK Student Climate Network said more than 200 events had been organised across the country.
Greta, who sparked the global climate movement where young people "strike" from going to school, said she never imagined it would take off so quickly.
She said she watched news of strikes in Australia and the Pacific before she went to bed in New York the night before.
The teenager called the large numbers of people protesting "a victory", adding: "I would never have predicted or believed that this was going to happen someday and so fast."
She said it was now up to world leaders to take action, and if they do not, they should "feel ashamed".
Labour leader Jeremy Corbyn told young people in the crowd in London that "you and a whole generation have brought the issue centre stage and I am absolutely delighted about that".
He criticised US President Donald Trump for failing to act on climate change and said he wanted to work with Brazil's President Jair Bolsonaro to preserve and protect the Amazon rainforest.
Green Party politician Caroline Lucas said: "It feels like there is a real uprising. It feels like there is a real sense from young people in particular that they simply won't wait any longer.
"It is their future that is at stake and our generation, my generation is responsible for not having done nearly enough to address that.
"They have enormous moral authority when they tell us that."
One of the protesters, Jessica Ahmed, a 16-year-old from north London, said "school is important but so is my future" -and called on the government to acknowledge the severity of the climate crisis.
"If politicians were taking the appropriate action we need and had been taking this action a long time ago when it was recognised the world was changing in a negative way, then I would not have to be skipping school," she added.
In Berlin, it was estimated 80,000 people gathered in front of the capital's landmark Brandenburg Gate, not far from Chancellor Angela Merkel's office where the cabinet was discussing final details of a plan to cut Germany's greenhouse gas emissions.
More than a million students from 1,800 public schools have been allowed to skip school in New York in order to protest.
In Africa, rallies were held in Johannesburg and the South African capital Pretoria, as well as Kenya's capital Nairobi.
The global protests come ahead of a summit at the UN next week that will urge countries to do more to avoid the worst effects of climate change.