The climate protesters have targeted the heart of the UK Government, taking to London hot spots such as Trafalgar Square and Westminster Bridge with loud steel drums, yoga mats and notable costumes.
Parliament Square was meanwhile empty of traffic except for police vans and bicycles, while helicopters circled overhead, as protesters created roadblocks on Victoria Street, Whitehall and the Mall.
They are demanding the Government takes urgent action on climate change and wildlife losses.
The group said many of the protesters were arrested as they blocked Victoria Embankment outside the Ministry of Defence.
Among those arrested by the Metropolitan Police was 81-year-old Sarah Lasenby, a retired social worker from Oxford.
She said:"It is imperative the government should take serious actions and put pressure on other states and global powers to radically reduce the use of fossil fuels."
As part of an "international rebellion" around the world, Extinction Rebellion kicked off two weeks of activities designed to disrupt the city.
In other European cities, including Berlin, activists blocked roads ahead of what is being described as widespread demonstrations.
Activists say they expect the protests to be as much as five times bigger than ones held in April, which brought major disruption to London and saw more than 1,100 arrests.
Protests are also being held outside Government departments, calling on authorities to outline what their plans are to tackle the climate emergency. There has been processions, marches and a sit-in at London City Airport.
Members of Extinction Rebellion said police confiscated six vehicles as well as gazebos, portable toilets and bean bags - and have since claimed the arrests were pre-emptive.
A protest last week saw activists spray fake blood from an old fire engine on the Treasury in protest at funding for fossil fuels.
Extinction Rebellion is calling on the Government to declare a climate and ecological emergency, to act immediately to halt wildlife loss and to reduce greenhouse gas emissions to net zero by 2025.
They want to see the Government create and be led by the decisions of a citizens' assembly on climate and ecological justice.