Tens of thousands of people have rallied in central London to demand world leaders take action to combat climate change.
Celebrities including pop singer Charlotte Church, actress Emma Thompson and designer Vivienne Westwood are among those at the climate march calling for politicians to take urgent steps on global warming.
It aims to put pressure on more than 50 world leaders gather in Paris for United Nations talks starting on Monday to discuss coordinated action to curb rising temperatures.
The London rally is expected to be the largest single rally in a weekend of action which will see almost 2,500 events take place around the world.
Campaigners want the Government and other countries to agree a deal that will shift the world to 100 per cent renewable energy and protect people from the impacts of climate change.
Campaigners dressed as polar bears and fish joined more sober marchers waving placards at the march, which has attracted people from across the UK and even further afield.
Sina Brown-Davis, an indigenous woman from Auckland in New Zealand, said she wanted "to put a face to the front-line impacts of climate change".
"Pacific people have contributed the least to climate change but we are paying the price with sea level rises and salination to our drinking water," she said.
"It is very much a life and death struggle for people in the Pacific at the moment."
The march began at Park Lane in West London at midday, and will continue through the streets to assemble for a rally at Millbank, just south of Parliament in the afternoon.
Numerous road closures have been out in place by authorities.
Actress and campaigner Emma Thompson told ITV News that the climate fight was "the bandwagon of the century" as she urged others to get involved.
She hailed the upcoming Paris climate talks as the biggest and most inclusive yet, saying it was due to "popular pressure on leaders in developing countries to come and join in with this, and also the willingness of leaders of developed countries to finally accept the climate science".
This is, as it were, the bandwagon of the century and everything is connected to it.
Labour leader Jeremy Corbyn told the crowds: "Those who are sitting around the tables in Paris have an enormous opportunity in front of them.
"Do not let them flake it or fool us. Make them understand that if we are to bequeath to future generations a world of flooding, a world of environmental disaster, a world where our children will not be able to live or eat properly then they will do nothing and allow the pollution of this planet to continue.
"If, however, they listen to the words of millions all around the world who are saying it is possible to reduce the level of emissions, it is possible to slow the rate of temperature change, it is possible to protect large parts of the environment of this planet, then they will have done something useful.
"Our message today is to them - 'Do what you are sent there to do. Do what you have been sent there on our behalf."