Extinction Rebellion said protests would continue throughout the week "escalating the creative disruption across the capital day by day".
Waterloo Bridge is a major bus route and the protestors from the group Extinction Rebellion delayed the journeys of far more public transport users than the vehicle drivers they claim should switch to more sustainable modes.
Hundreds of people gathered outside Oxford Circus Tube station around a bright pink boat, where some used makeshift devices to lock their arms together.
Demonstrators hold a banner during a climate protest in Parliament Square in London, Monday, April 15, 2019.
Thousands of people are expected to take to the streets of central London today, blocking the city's busiest roads and bridges to raise the alarm over a mounting climate crisis.
The campaign cites the civil rights and suffragette movements as inspiration and is backed by senior scientists and academics, including the former archbishop of Canterbury Rowan Williams.
A TfL spokesman said: "The safety of our customers and staff is our number one priority and we're working closely with the police to manage the impact on London's transport network".
"We don't want to disrupt people, but our government's failure over the last 30 years leaves us no choice", an Extinction Rebellion spokesperson said.
Extinction Rebellion (XR), an environmentalist group responsible for causing scenes in the House of Commons earlier this month when semi-naked activists stripped off in Parliament as MPs tried to debate Brexit, claim they intend to occupy the roads for at least 72 hours. "We wish to make peace with ourselves by making peace with our neighbour Earth and with our God".
Organisers said: "The International Rebellion begins and Extinction Rebellion will be bringing London to a standstill for up to two weeks".
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 United Kingdom for what is described as an International Rebellion.