Thousands of demonstrators descended on central London on day 2 of four days of environmental protests dubbed ‘The Big One’.
More than 200 groups including Extinction Rebellion are in the capital with a shared message calling for more action on climate change.
Many marched through the streets brandishing placards demanding governments across the globe step up their efforts to bring in policies to protect the planet.
Wildlife presenter Chris Packham made a rallying call for “every last person who cares” as he joined the demonstrators on Saturday.
The 61-year-old broadcaster spoke to the crowd from a stage close to Parliament Square, Westminster.
Around 50,000 people are expected to join the action between April 21-24, which has support from more organisations including Greenpeace and Friends of the Earth.
On Saturday, which is also the 53rd global Earth Day, Packham told protesters their “mission” was to “build as wide a community as possible”.
He said: “Our planet is in crisis and if we don’t take action then we will not protect that life, which includes us.
“One thing is clear and that is that we need to step up… We want every last person who cares to get involved, because caring is not enough.”
Packham commended two Just Stop Oil protesters who were jailed on Friday after scaling the Dartford Crossing bridge in Kent for “sacrificing” their freedom through the “enormous act of bravery”.
Morgan Trowland, 40, was imprisoned for three years over the stunt, while Marcus Decker, 34, was jailed for two years and seven months.
By contrast to this protest, “The Big One” aims to cause minimal disruption so that it is accessible to all, and many activists attended with their children to inspire the next generation to join their ranks.
Edwina Lawson, 42, who was at Parliament Square with her children – aged three and six, said XR’s protests were “easier” for families to support than Just Stop Oil, but she felt more radical activists were “very very brave”.
The GP from Tottenham, north London, told the PA news agency: “Like everyone else, I’m really really concerned that the powers that be are not paying attention to the climate crisis and things are getting worse.”
Indicating to her children, she said: “They’re the ones who are going to inherit the lack of care that’s being taken now.
“I think there’s so much positive that could be done about the energy that we use, and you could create so many jobs through renewables and I think changing energy sources is the number one demand.”
Veteran XR protester Jo Clark, 39, also from Tottenham, said she felt “heartened to see so many people come out in support”.
Ms Clark, who works in the arts and was holding her one-year-old toddler, said schools were failing to teach children about climate change and she wanted the Government to “buck up and deal with it”.
She told PA: “There’s still plenty of opportunity to deal with the climate crisis and it’s not being done by central Government in any way, shape or form.
“We declared a climate emergency in legislation but there is nothing that’s being done to meet those targets.
“We’re continuing to licence new gas and oil which is going to continue to drive us over the edge… It is scary, but buck up and deal with it.”
Beyond Parliament Square, thousands more activists staged a “die-in” by laying on the pavement at The Mall – aiming to represent the potential future extinction of humanity due to global warming.
Many people also wore fancy dress, including the distinctive red-robed army of XR protesters who frequently turn up to the protests, while others wore masks depicting the King, Prime Minister Rishi Sunak, and various animals.
London Mayor Sadiq Khan said he “passionately believes that this climate emergency has got to be tackled” and urged XR to “protest in a way that is peaceful, lawful and safe”.
On Sunday, protesters will share the capital’s streets with tens of thousands of runners taking part in the TCS London Marathon.
Mr Khan said he hopes the sporting event is “a huge success” and that “there is no disruption by XR or anybody else”.
XR has said it has worked with TCS organisers to ensure the marathon will not be disrupted.