Protesters plan to block traffic at four London locations "around the clock" to force the Government to take urgent action on climate change and wildlife declines.
Campaign group Extinction Rebellion said it will take to the streets at Marble Arch, Oxford Circus, Waterloo Bridge and Parliament Square from Monday April 15 to cause disruption and force the Government to act.
Thousands of people will converge on the four busy locations, peacefully blocking traffic and creating a "festival" of action including people's assemblies, performances, talks, workshops and food, the group said.
Extinction Rebellion is calling on the Government to declare a climate and ecological emergency, to act to halt wildlife loss and bring greenhouse gases to net zero by 2025, and create a citizens' assembly to deliver action on the environment.
Coaches will bring people from around the country to the protest, where they will be joined by cyclists and marchers who have travelled to the capital by bike and on foot.
The direct action campaign calling for governments to urgently tackle the "climate and ecological emergency" has spread into an international movement and is backed by celebrities, academics and writers.
Actress and activist Dame Emma Thompson said: "Our Government has signed agreement after agreement and broken every single promise they made with staggering regularity.
"It is time to stand up and save our home. There will be talks, politics, music, arts. It's gonna be a lot of fun, but be prepared to stay. Because now's the time to save the planet. As we all know, there is no planet B. Be there."
Jayne Forbes of Extinction Rebellion warned that the window to reduce carbon emissions and halt the "sixth mass extinction" was closing rapidly.
"Extinction Rebellion calls on everyone, regardless of your political or religious or cultural beliefs, to join us as we peacefully disrupt for the future of humanity and for all life on Earth.
"If even a small part of you is sitting at home wondering what to do about the climate and ecological emergency, this is what we need to do. This is the best shot we have, we can't get a new planet."
She urged people to book at least two weeks off work, if possible, and bring their tents and families to "rebel for life on Earth".
Emily Beament is the environment correspondent for the Press Association.