Some mourners shouted “hip hip hooray” and “God save the King” as Charles passed.
One woman held up a Paddington Bear toy to Charles; the fictional bear has become associated with the Queen since she appeared in a sketch alongside the character during her Platinum Jubilee celebrations.
People have been queuing for hours to view the Queen Elizabeth II’s coffin since she began lying-in-state at Westminster Hall on Wednesday.
The line was nearing total capacity on Saturday, the government said. At lunchtime on Saturday, the government’s queue tracker said the current wait time was 14 hours.
Earlier on Saturday, Charles III visited Metropolitan Police headquarters in the Lambeth borough of London to thank police and emergency services officials involved in the planning and implementation of events since the death of the late Queen.
Monday’s funeral for the Queen will be the “largest single policing event” that London’s Metropolitan Police force has ever undertaken, Deputy Assistant Commissioner Stuart Cundy said during a media briefing on Friday.
The Queen’s grandchildren — including Princes William and Harry — are expected to stand vigil by her coffin later on Saturday.
On Sunday, King Charles will host a reception at Buckingham Palace for “Heads of State and official overseas guests” ahead of the state funeral for the late Queen.
The Duke and Duchess of Sussex, Prince Harry and Meghan, received an invitation to that reception by mistake, a source with knowledge of what happened told CNN.
As an official state occasion, the Palace said the King would be accompanied by working members of the Royal Family only. The source told CNN that they “imagined” that an administration error had occurred. The couple was not “disinvited” from the reception, as some media outlets have reported.
A spokesperson for the Sussexes did not comment.