Thousands of protesters have descend on central London for the Million Masked March, despite Scotland Yard imposing strict restrictions on the event.
Supporters of the hacking collective Anonymous began marching on Trafalgar Square on Saturday with scores of police officers maintaining a tight perimeter.
The group's agenda is broadly anti-capitalist and pro-civil liberty, with many of the demonstrators wearing Guy Fawkes masks in an effort to recreate the final scene of cult film V For Vendetta. It is one of many similar marches held worldwide on 5 November.
The march began peacefully, with several demonstrators climbing the base of Nelson's column and chanting "one solution, revolution".
A small number of fire works have reportedly been set off in the crowd and some demonstrators have marched off the pre-organised route, according to reports in Twitter.
Metropolitan Police issued a warning before the event that “masked criminals seeking to run amok” will be arrested if the protest turns violent after last year’s march saw ugly scenes with missiles and fireworks thrown at police.
Police said last year protesters abandoned an agreed route and timetable for the demonstration and thousands of riot police and mounted officers were deployed to contain crowds after the largely peaceful protest at Trafalgar Square and Parliament Square dispersed across the centre of the capital.
Four officers and six police horses were injured and some protesters attempted to set a police car on fire.
More than 1,000 people are believed to have attended the march in 2015 and there were more than 50 arrests.
Police have imposed conditions on this year's march, limiting it to a three-hour period between 6pm and 9pm on a prescribed route between Trafalgar Square and Whitehall.
Any static protest must only take place in Trafalgar Square, Richmond Terrace and Parliament Square, and the Met has warned that anyone breaching the conditions could be arrested for public order offences.
Nearly 20,000 people had indicated they would attend on the event's Facebook page, which defended the action saying "the police are not your friends".
Additional reporting by Press Association
