Millions of people around the world are expected to take part in what could be the largest climate protest in history. British students are preparing to walk out of lessons and lectures and adults are being encouraged to join them as they strike.
Protests inspired by the teenage Swedish activist Greta Thunberg are planned in around 150 countries as people demand world leaders take immediate action to limit the harmful effects of manmade climate change ahead of a environmental summit at the United Nations in New York on Monday, as the UN General Assembly opens.
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Tweeting a photo from the climate strike in London, Jeremy Corbyn, the Labour leader, said:
Extinction Rebellion UK, which has held numerous climate and environment protests around the UK this year, said it "stands in solidarity" with the young climate strikers.
The group said many of its members were joining the strikes and holding their own events, including a choir and "kids' space" in Victoria Tower Gardens, Westminster, and claiming the streets outside King's College London as part of freshers' week rebellion events.
XR Universities - an Extinction Rebellion group - has called for an overhaul of degrees so that they address the impact of climate change. UK universities must take immediate action in response to the climate crisis, the group said.
The protests have been inspired by the 16-year-old Swedish activist Greta Thunberg, who urged US senators to learn from the sacrifices of Martin Luther King and other civil rights activists in the fight against climate change:
Greta Thunberg: I have a dream that the powerful will take the climate crisis seriouslyIn a highly anticipated speech in Congress after travelling half the way across the Atlantic by boat, Greta Thunberg urges US senators to learn from the sacrifices of Martin Luther King and other civil rights activists in the fight against climate change. Here is the transcript
At 1pm, the student strikers are planning to let off alarm clocks across the UK, and are encouraging businesses to set off their fire alarms at the same time in support.
Jake Woodier, campaign co-ordinator at UK Student Climate Network said: "Young people across the world have taken the lead in highlighting the need for urgent climate action over the past year.
"They are calling for adults to join them for the Global Climate Strike, just three days before the UN climate action summit to pressure our governments to act to tackle the climate crisis.
"Raise The Alarm will help draw attention to the climate emergency in workplaces across the breadth of the UK.
"We understand it's simply not feasible for many employees to take a day off to participate in a strike, but that doesn't mean they can't have a voice.
"By hosting their fire drills at 1pm on 20 September, working adults have the chance to demonstrate their concern about climate change."
Thousands of people are marching around Parliament Square before heading on to Millbank, Phoebe Weston writes.
It is already starting to get hot and there is a huge amount of energy from young people chanting "this is what democracy looks like" and "climate justice now".
Friends of the Earth have someone dressed up as "the statue of taking liberties":
A medical student from Extinction Rebellion Universities has explained her reasons for joining the strike, she wants more education on climate change for students and members of the public:
The protest at Millbank is packed with people of all ages, Phoebe Weston reports.
There are people from all types of organisations - unions, charities, migrant groups. The atmosphere was positive, feeling a bit like a festival with serious undertones.
Quite a few posters were on display supporting the Amazon.
Friends of the Earth campaigner Aaron Kiely tells Phoebe Weston the government is "letting us down" on climate action:
Dozens of Filipino activists have marched in Manila to honour the memory of activists in the Philippines who were killed for defending the environment.
They marched to the offices of the Environment and Natural Resources Department, then staged a die-in protest while holding a banner saying 'Stop the killings. Defend the environment defenders now!"
The group Global Witness said the Philippines had the highest number of killings of environmental defenders of any country in 2018, with at least 30 murdered.
A separate rally organised by various student groups gathered in the afternoon at the state university. Hundreds participated as each of the students bunched together to hold up placards forming an image of the earth, with a big sign that said: "There is no Planet B."
The Metropolitan Police said two people had been arrested for breaching conditions imposed on the protesters which dictate they must gather in a specific place in Westminster.
In a tweet from the MPS Events account, the force said:
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