The father of British Prime Minister Boris Johnson has joined climate protesters in London, after his son urged the demonstrators to pack up their "hemp-smelling bivouacs" and leave.

Stanley Johnson told Extinction Rebellion demonstrators they had "exactly the right things in mind" with their demand to slash carbon emissions to zero.

Speaking in front of hundreds at one of the event's climate change panels in Trafalgar Square, he said the eco-movement was "tremendously important".

"It is absolutely clear to me that we have been moving far too slowly on the climate change issue," he said.

More than 500 people have been arrested in London since protesters began blocking roads and bridges on Monday, part of a global wave of protests that have also hit New York, Paris, Berlin and Madrid as well as cities in Australia.

Extinction Rebellion demonstrators took to the streets of London calling for governments to do more to tackle climate change. ( ABC News: Lara Hyams )

In London, protesters set up tents and took part in "sit-ins" while ignoring police orders to move from the area.

Organisers gave demonstrators handouts with legal guidance in case they were arrested during the protest.

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Officers forcibly removed several people while others began dismantling makeshift structures.

Local police recruited officers from across the country to assist with breaking up demonstrations.

Boris Johnson has called the protesters "uncooperative crusties" who should abandon their "hemp-smelling bivouacs".

Stanley Johnson said: "I wear that badge with pride."

A police officer attends to a demonstrator lying in a tent on the ground during London's Exctinction Rebellion protest. ( ABC News: Lara Hyams )

ABC/AP