A Transport for London worker appealed to the group to move their protest elsewhere, but the activists refused.
WiFi has been shut down across the Tube network in a bid to deter demonstrators blocking Underground services.
There are now four roadblocks continuing after Picadilly Circus was reopened to traffic. The group Extinction Rebellion is calling for a week of civil disobedience against what it says is the failure to tackle the causes of climate change.
The group says climate breakdown threatens all life on Earth, and so it is rebelling against politicians who "have failed us", to provoke radical change that will stave off a climate emergency.
"The safety of our customers and staff is our number one priority and we're already working closely with the police to manage the impact on London's transport network".
"During the next 24 hours, these intelligence-led patrols will be in place to help keep everyone safe and to ensure that disruption is kept to a minimum".
The events in London are part of an global "climate rebellion" organised by Extinction Rebellion. In The Hague on Tuesday, activists occupied the worldwide criminal court building.
Activist Katy Fowler, 39, from Machynlleth in Wales, said reaction from the public had been very positive.
Demonstrators began blocking off a bridge and major central road junctions on Monday at the start of a civil disobedience campaign that also saw action in other parts of Europe.
The protesters maintain that governments are not taking climate change seriously enough, and are demanding that a state of "climate and ecological emergency" be declared.
"In order to impose this condition, the Met required evidence that serious disruption was being caused to communities in London".
"We so far have 55 bus routes closed and 500,000 people affected as a result", the police said.