Organisers estimate hundreds of thousands of Scottish independence supporters have marched through Edinburgh, with calls intensifying for a fresh vote on Scotland breaking away from the United Kingdom as a possible no-deal Brexit looms.

Key points: Rally organisers said a breakaway from the UK had been given fresh momentum by the ongoing wrangle over Brexit

Rally organisers said a breakaway from the UK had been given fresh momentum by the ongoing wrangle over Brexit The majority of Scots voted to remain in the EU in the 2016 Brexit referendum

The majority of Scots voted to remain in the EU in the 2016 Brexit referendum Hundreds of thousands of demonstrators waved blue flags and played bagpipes as they wound through the city

Rally organisers All Under One Banner (AUOB) said more than 200,000 people — some wearing kilts and playing bagpipes — filled the Scottish capital's winding streets, far exceeding their turnout predictions.

As a sea of blue Saltire flags flowed through the heart of the city and its famous Royal Mile, demonstrators chanted: "What do we want? Independence!"

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Although Scotland voted against independence from the UK in a referendum in 2014, organisers said a breakaway from the United Kingdom had been given fresh momentum by the ongoing wrangle over Brexit.

The majority of Scots voted to remain in the European Union in the 2016 Brexit referendum, in which the majority of Britons voted to leave.

Harry Baird, an apprentice marine engineer taking part in the rally, said he wanted to join what he believed would be the biggest rally in the country's history.

"There's a lot more [people] that I thought I would see, to be honest," the 19-year-old told the BBC.

"[I want] more radical and instant Scottish independence. Any change from what it is now would be worth it," he said.

Lawyer and Scottish National Party (SNP) politician Joanna Cherry, who was behind one of the successful legal challenges to Prime Minister Boris Johnson's decision to suspend Parliament, was also present at the march.

A demonstrator plays the accordion as he waits to attend a pro-independence march through the centre of Edinburgh, Scotland. ( AFP: Andy Buchanan )

She was one of the main backers of a law passed last month forcing Mr Johnson to ask the EU for more time to avoid crashing out of the EU without a deal.

Scotland's First Minister, Nicola Sturgeon, did not join the event but tweeted that she was there "in spirit".

"Be in no doubt — independence is coming," she said.

Ms Sturgeon has argued that Brexit will devastate the economy and wants a second independence referendum in 2021, while nationalists argue that some people voted against independence thinking it would guarantee their place inside the EU.

Neither Police Scotland nor the City of Edinburgh Council was able to give an independent estimate of the number of people at the rally.

Although Scotland voted against independence from the UK in a referendum in 2014, organisers said a breakaway from the UK has been given fresh momentum by the ongoing wrangle over Brexit. ( NurPhoto: Ewan Bootman )

Following a similar event last year, AUOB said there was a crowd of 100,000 but the local council later estimated that 20,000 marchers took part.

A small number of pro-Union protesters carrying Union Jack flags staged a counter-demonstration in central Edinburgh.

ABC/AFP