The protests are part of a global campaign organised by the British climate group Extinction Rebellion, with demonstrations planned in 80 cities across 33 countries in the coming days.
The Metropolitan Police said half a million people have been affected with 55 bus routes diverted.
Expect to see protesters gluing or locking themselves to gates, benches, turnstiles and other street furniture to bring intersections and streets to a standstill today. "It's like a world war".
Extinction Rebellion is demanding the Government declare a climate and ecological emergency and reduce greenhouse gas emissions to net zero by 2025. "We have to go on to a war footing".
The campaigners, under the label Extinction Rebellion, had camped overnight at Waterloo Bridge, Parliament Square and Oxford Circus.
Financial Times also noted that Extinction Rebellion makes a point of having demonstrators arrested; in the last six months or so, over 200 people affiliated with the movement have been arrested.
"This crisis is only going to get worse ..." Glass in the building's revolving entrance door was smashed, which the campaigners claimed would cause £6,000 worth of damage. "We must act now".
Extinction Rebellion said "over 100 courageous rebels" had been arrested in total.
The protests were organised by the campaign group Extinction Rebellion, which was established past year in Britain by academics and has become one of the world's fastest-growing environmental movements.
Police said five of those arrested were detained after the Shell building near the River Thames was targeted. A police officer on the bridge said the Met could impose limits on assembly if they felt there was a serious risk of disruption or to public order.
Among the protestors was a group of cyclists from East Anglia who made the 155 mile journey from London to Norwich by bicycle.
Blythe Pepino, 34, from Hereford, said: "The objective is to maintain the disruption on the bridge to bring the Government to the table and talk about the climate crisis".
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