Today thousands of climate activists blocked parts of central London, Marble Arch, Oxford Circus and Waterloo Bridge aiming to force the government to tackle climate change with more affords.

Activists sang songs and held signs that read “There is no Planet B” and “Extinction is forever” at some of the capital’s most known locations.

Roadblocks will continue night and day at each site and the demonstrators say the protests could last at least a week.

The protests are being led by the British climate group Extinction Rebellion and will involve demonstrations in 33 countries around the world over the coming days.

“I realised that signing petitions and writing letters was not going to be enough. Real action is needed,” said Diana McCann, 66, a retired wine trader from south London, holding a banner in the middle of a traffic-free road. “It’s like a world war. We have to go on to a war footing.”

Extinction Rebellion, which generated headlines with a semi-nude protest in the House of Commons earlier this month, has warned its members that some of them could be arrested for taking part in non-violent civil disobedience.

The group is demanding the government declare a climate and ecological emergency, reduce greenhouse gas emissions to net zero by 2025 and create a citizen’s assembly of members of the public to lead on decisions to address climate change.

At the Shell building near the River Thames, two protesters scaled up scaffolding writing ‘Shell Knows!’ in red paint on the front of the building and three protesters glued their hands to the revolving doors at the entrance.

At Oxford Circus, protesters unveiled a pink boat that says “TELL THE TRUTH” and on Waterloo Bridge demonstrators brought trees, hanging baskets and skate ramps.

The protest had a festive atmosphere, with many families in attendance, and a low police presence.

Extinction Rebellion wrote to Prime Minister Theresa May on Monday outlining their demands and asking for face-to-face talks, warning that they will escalate their disruptive actions over the coming weeks unless the government acts.

“Make no mistake, people are already dying,” the letter states. “In the majority world, indigenous communities are now on the brink of extinction. This crisis is only going to get worse Prime minister, you cannot ignore this crisis any longer. We must act now.”

Protests organisers advised to anyone willing to attend, to refrain from using drugs and alcohol, and asked to treat the public with respect.