Thousands of protesters have brought London to a standstill to voice their opposition to Boris Johnson’s controversial plan to suspend Parliament.
From noon today, demonstrators stretched across Whitehall as they gathered outside the gates of Number 10.
Demonstrators can be heard chanting "Boris Johnson, shame on you" and "stop the coup”.
When speeches concluded at Whitehall just before 2pm, a number of protesters blocked Westminster Bridge.
Six police vans have arrived at the bridge and are reportedly threatening to arrest demonstrators obstructing access, according to reports.
Others are shouting and "our democracy and parliament is under attack", bringing foot and vehicle traffic along the crossing to a halt.
Marchers on the bridge shouted: "If you shut down our Parliament, we shut down your bridge!"
Anti-Brexit campaign group Another Europe Is Possible has planned 32 #StopTheCoup protests to take place in England, Scotland and Wales.
Demonstrations are taking place across the UK as thousands have taken to the streets in cities including Manchester, Leeds, York and Belfast.
One Twitter user wrote: “Absolute scenes on Westminster Bridge!
“Downing Street, Waterloo, Trafalgar Square are also shut down.
“100.000 people are here, young and old, Remainers and Leavers, united and determined to #StopTheCoup.”
A small group of counter-protesters, marching in support of the prime minister, also arrived in Westminster.
Mr Johnson's plan to prorogue Parliament prompted an angry backlash from MPs and opponents of a no-deal Brexit when he announced it on Wednesday.
Left-wing group Momentum called on its members to "occupy bridges and blockade roads" in conjunction with unrest on the streets.
Shadow home secretary Diane Abbott addressed the crowd near Number 10 with a message from Jeremy Corbyn, whom she said sent his support to demonstrators.
"We are here outside 10 Downing Street trying to get Boris Johnson's attention, but let me tell you, before too long Jeremy Corbyn will be in 10 Downing Street and Boris will be gone," she said.
The Labour leader plans to speak at a rally in Salford on Monday.
He said: “The public outrage at Boris Johnson shutting down democracy has been deafening. People are right to take to the streets – and I encourage everyone to join the demonstrations in London and across the country.”
Shadow chancellor John McDonnell urged Labour MPs to join the nationwide protest, calling the Prime Minister's decision to close Parliament for up to five weeks an attempt "to shut down democracy".
"As elected Labour MPs across the country represent their constituents by joining in these protests, I urge other MPs to think of their constituents whose jobs and livelihoods will be put at risk in a no-deal Brexit," Mr McDonnell said.
"If Boris Johnson wants a mandate, then he should call a general election and put it to the people."
The shadow chancellor is due to address youth movements at the main London protest at Downing Street on Saturday.
Other demonstrations are being held in cities including Birmingham, Manchester, Liverpool, Glasgow, Swansea, Leeds, Belfast, Bristol and Aberdeen.
Hundreds of protesters blowing of whistles and bang of a drum echoed around the surrounding Government buildings, as many carried placards and European Union flags.
More than 1,000 people gathered in the centre of York to listen to speakers outside the famous Bettys tea rooms and The Ivy restaurant. Many of those in St Helen's Square were carrying banners as well as EU and Yorkshire flags and hats.
There are rallies in smaller places including Bodmin, Cornwall, and Clotheroe, Lancashire, as well as Amsterdam's Dam Square and the outside the British Embassy in Riga, Latvia.
Further mass demonstrations, organised by the People's Assembly Against Austerity, are planned to take place on Tuesday to coincide with MPs returning to Westminster.
Both pro and anti-Brexit protesters clashed on Wednesday after the Queen approved an order that will see Parliament suspended for more than one month.
Laura Parker, Momentum's national co-ordinator, called the proroguing of Parliament a "loophole in our flawed democracy".
"There are thousands of people from all over the UK and across the political spectrum who will protest to stop Johnson closing the doors on our democracy," she said.
"No-one voted for this, and it's clear we need to urgently redesign our system to rebalance power away from the top."
The calls for protests come as a petition against the Prime Minister's plan to suspend Parliament racked up more than 1.64 million signatures early on Saturday morning.