The group Extinction Rebellion is organizing several weeks of civil disobedience against what it says is the failure to tackle the causes of climate change.
Chief Supt. Colin Wingrove said police were dealing with several demonstrations in central London which had had a significant impact on public transit. He said 55 bus routes had to be shut down and roughly 500,000 people had been affected.
"At this time, ongoing demonstrations are causing serious disruptions to public transport, local businesses and Londoners who wish to go about their daily business," he said, adding that police expect the protests to last several weeks.
On Monday, demonstrators blocked sites including Waterloo Bridge over the River Thames, the busy Oxford Circus intersection and Parliament Square, and vandalized the headquarters of oil company Shell.
After hours of disruption, police ordered the group to confine protests to Marble Arch, beside Hyde Park. Scores of demonstrators who refused to move were arrested - 209 by Tuesday evening - and traffic was slowed in several parts of central London.
Many of the arrests were made as protesters tried to block Waterloo Bridge.
Extinction Rebellion said protests would continue.
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