The Metropolitan Police said officers would be used from across the service to provide a “proportionate” response to the protests, which balanced the right to a peaceful protest while ensuring disruption to communities was kept to a minimum.
A spokesman urged travellers to allow extra journey time as road closures and disruptions to the travel network were expected.
It comes as part of attempts to force the Government to declare a climate emergency. Earlier this month, several activists stripped semi-naked in the House of Commons during a Brexit debate.
The movement has received support from actress and activist Dame Emma Thompson and former archbishop of Canterbury Dr Rowan Williams.
Speaking at a meditation on the eve of the protests Dr Williams said humans had declared war on nature.
He said: “We are here tonight to declare that we do not wish to be at war. We wish to make peace with ourselves by making peace with our neighbour Earth and with our God.”
Thompson has previously said of the demonstrations: “It is time to stand up and save our home.”
Organisers said: “The International Rebellion begins and Extinction Rebellion will be bringing London to a standstill for up to two weeks.
“They will be blocking five of the city’s busiest and most iconic locations in a non-violent, peaceful act of rebellion where they invite people to join them for several days of creative, artist-led resistance.”
Demonstrators arrived at London’s Hyde Park on Sunday, some having journeyed to the city on foot in recent weeks from various parts of the UK for what is described as an “International Rebellion”.