Hundreds of soldiers have taken part in early-morning rehearsals in Windsor as preparations continue for the Queen's funeral.
Rehearsals at Westminster Abbey and Windsor were being held as world leaders started to arrive in London.
Marching bands playing music and Grenadier Guards flanking a hearse were seen rehearsing in the early hours in Windsor.
After Monday's service at Westminster Abbey, the late monarch's coffin will be driven from London to the Berkshire town in the state hearse before travelling in procession to St George's Chapel at Windsor Castle via the Long Walk.
As the lying in state continues in Westminster Hall, the queue of mourners waiting to see the monarch's coffin is now expected to take around 24 hours from the back to the front.
So long has it become, the Department for Digital, Culture, Media and Sport is now warning people not to travel to join it - and to check back later on Saturday for updates on wait times.
Representatives from the Commonwealth nations have been invited to pay their respects, and heads of state from around the world are arriving throughout the weekend, both to attend the Queen's funeral, and to sign a book of condolences.
Meanwhile, King Charles will meet the chiefs of staff at Buckingham Palace before visiting police headquarters, where he will thank representatives from all the emergency services involved in the planning and delivery of the events during the mourning period.
He will also attend, with the Queen Consort, a lunch for governors general - the people who represent the monarch in overseas realms - at the palace.
Also on Saturday, the Queen's grandchildren will take their turn standing in vigil around her coffin.
The Prince of Wales will stand at the head, the Duke of Sussex at the foot.
William will be flanked by his cousins Zara Tindall and Peter Philips - the children of the Princess Royal - while Harry will be with the Duke of York's daughters Princesses Beatrice and Eugenie.
The Earl of Wessex's children Lady Louise and Viscount Severn will stand near the middle.
Forecasters say the sun is expected to shine on those waiting in the queue and those already securing the best spots for the funeral procession. After a cold start, Saturday should see long, sunny spells with maximum temperatures of 17C (62F), they predict.
Codenamed Operation London Bridge, arrangements for the Queen's death have been carefully pored over for years, with the monarch herself overseeing and approving every detail before her passing.
However, the exact details were kept under wraps until the sitting sovereign, King Charles III, gave it his final seal of approval.
Monday's funeral is at Westminster Abbey, one of London's most recognisable landmarks and near the Palace of Westminster.
It has been the setting for every coronation since 1066, and was where the then-Princess Elizabeth married Prince Philip in 1947.