In Sydney, Australia, they sailed a ship along the harbour flying banners with their message. In Ho Chi Minh City, Vietnam, youth groups organised flash mobs to raise awareness. And in Durham, here in the UK, activists locked themselves onto mining machinery in a bid to close a pit for the day.

Hundreds of thousands of climate change protestors are gathering at some 850 events across 90 countries – and seven continents – in what is one of the biggest ever days of global action highlighting the issue.

They are marching in cities from Kathmandu to Copenhagen, Lagos to Lisbon, Bogota to Berlin.

Support has even come from Antarctica, where the astrobiologist Cyprien Verseux has pictured himself holding up a banner featuring the day’s official moniker, Rise for Climate.

Later, things will climax with the painting of the world’s biggest street mural in San Francisco.

“Climate change is the defining issue of our time, it is a crisis of democracy, justice and human rights,” said May Boeve, executive director of 350.org, the New York-based campaign group behind the day. “The climate movement is made stronger by its sister movements: for human rights, economic justice, democracy, and much more.

“This weekend Rise for Climate will demonstrate the growing strength and diversity of the climate movement. People power is accelerating the change we need to see, and usher in a new era of clean air and better health. Communities everywhere will show loudly and clearly what is expected from decision-makers to deliver on real climate leadership and build a fossil-free economy.”

In the UK, events are being held in places ranging from London to Wigan, Bradford to County Durham.

As part of the latter, activists have locked themselves onto mining machinery at Field House opencast pit in a bid to stop work for the day. Another group has also stationed themselves at the nearby Bradley opencast site for the same purpose. The protesters also want to draw attention to the campaign to fight the opening of a new mine in the nearby Pont Valley.

“We take direct action to challenge the destructive fossil fuel industry,” the groups said in a statement. “We stand in solidarity with the locals and protectors at Pont Valley, and those on the front lines fighting the fossil fuel industry globally.”

The events come ahead of the Global Climate Action Summit, which starts in San Francisco next week and will see politicians and city leaders from around the world gather to discuss the climate crisis.