Essex Police has sent officers to the London Extinction Rebellion protests.
The force confirmed it has sent officers "to support the Metropolitan Police under national mutual aid protocols".
Since Monday, climate change demonstrators have occupied Oxford Circus, Waterloo Bridge and Parliament Square.
The Met says 715 people have been arrested and 28 have been charged.
Dozens of people are in Oxford Circus, despite being told by police to move.
The Met told the BBC said it would continue to liaise with protesters and encouraged them to go to Marble Arch.
A spokesman told the BBC: "One thing that is unusual about this demonstration is the willingness of those participating to be arrested and also their lack of resistance to the arrests."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article