Huge crowds are expected to line the route as the coffin is taken through the streets tomorrow from Buckingham Palace to Westminster Hall to lie in state.
In preparation today, a black coffin was placed on a gun carriage and, at around 4am, the procession was ordered to march.
The carriage, pulled by seven black horses, made its way via Queen’s Gardens, The Mall, Whitehall, Parliament Street, Parliament Square and New Palace Yard.
Many of central London’s streets were sealed off for the massive operation.
Final preparations for events in the capital following the death of the Queen are taking place before she is flown from Edinburgh this evening.
The procession will take place tomorrow afternoon, and then Queen’s coffin will then rest in Westminster until her funeral on Monday.
People will have the chance to file past her coffin and pay their respects – with thousands already queueing overnight to do so in Edinburgh.
Today’s rehearsal began outside Buckingham Palace, with the horse-drawn carriage of the King’s Troop Royal Horse Artillery being led along the route it will take for real tomorrow.
The Queen’s coffin will remain in the Bow Room at Buckingham Palace tonight, with the public invited to pay their respects from 5pm tomorrow after the procession concludes.
The real procession begins at 2.22pm tomorrow, and it will last 38 minutes.
King Charles III, members of the royal family and senior staff of the Queen and King’s households are expected to walk behind the coffin.
The rehearsal, which took place before the sun came up, saw people standing in for them.
Given the time, only a few onlookers were present for the military spectacular, with some finding themselves there by chance.
However, one small group were camping outside Buckingham Palace.
John Lowell, from Streatham, south London, said he was ‘devastated’ by the news of the Queen’s death, adding: ‘We are all broken-hearted. I can’t take it in.’
His friend, Sky London, said they have been camping since Thursday ‘so we can get a good view of things’ and insisted they will not leave until after the funeral, so that they can pay their ‘respects’.
He added: ‘Ten days (of camping) against a 70-year reign is only a fraction.’
People have been warned not to wait or camp along the route where the Queen’s coffin will be taken for the lying in state.
Viewing areas along the route with limited capacity will open at 11am tomorrow, with people admitted in order of arrival time amid expected long queues, the Department for Digital, Culture, Media and Sport (DCMS) said.
The Queen’s coffin will remain in Westminster Hall until Monday, when it will be taken in procession from the Palace of Westminster to Westminster Abbey for the state funeral service.
Members of the public will have the opportunity to visit Westminster Hall to pay their respects during the lying in state but security staff said the queue is likely to snake for miles, potentially all the way along the River Thames to Tower Bridge.