Police say they have arrested more than 120 people after climate change protesters blocked major bridges and intersections in central London, bringing traffic to a standstill.

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 a number of 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 122 by early Tuesday afternoon and traffic movement was slowed in several parts of central London.

Extinction Rebellion said "over 100 brave rebels'' had been arrested. It said protests would continue.