Climate change activists climbed the outside of the headquarters of the City of London's government on Sunday as they began two weeks of protests focused on the capital's financial district.

About 200 demonstrators from the group Extinction Rebellion targeted the medieval Guildhall, the home of the City of London Corporation, which governs the city's historic financial centre.

Three activists climbed the facade of the ornate Guildhall, parts of which date back to the 15th Century, lit red flares and displayed a banner that said: "co-liberation-freedom together".

Extinction Rebellion, which caused days of traffic chaos in London two years ago, said it is targeting the city's financial district, which they blame for helping to fuel climate change.

The group wants an emergency response from governments and a mass move away from polluting industries to avert the worst scenarios of devastation outlined by scientists.

Extinction Rebellion brought much of central London to a standstill during 11 days of action in 2019, bringing its cause to the fore but also provoking criticism from some politicians who said the police had been too tolerant.

The City of London is the smallest local authority in Britain, and unlike most conventional British councils, officially declares its job is to reinforce the importance of financial services to the British economy.

It claims to be the oldest, continuous representative local government in the world, running the area that is home to the Bank of England and St Paul's Cathedral for at least a thousand years.