World leaders and mourners were arriving in London on Sunday for the state funeral of Queen Elizabeth II as a security net tightened around the capital and tens of thousands of people waited in line to say their own goodbyes.
Snipers, facial recognition technology, drones, horses and dogs are all in place to enhance security around both grieving crowds and heads of state.
Grieving citizens were on Sunday queuing for hours to see Queen Elizabeth, who will be lying in state until 6.30am on Monday, in her coffin at Westminster Hall, central London.
Charles was meeting some of the world leaders, who are in the city for the funeral.
About 26,000 people an hour passed through security barriers at the hall on their last steps of a kilometres-long queue to see the queen, who was 96 when she died, lying in state.
The area of Westminster around the Houses of Parliament is usually a highly secure ring of steel, well equipped with security cameras and antiterror measures. By Sunday, security had been stepped up even more.
Additional officers have been drafted in from across the UK, as well the Channel Islands and Gibraltar.
Close protection officers are shielding world leaders, and their partners, from the 185 countries with which Britain has full diplomatic ties — the largest close protection event for British police and estimated to be the biggest in the world.
Heads of state are expected to meet at a west London location where they will be taken by bus to Westminster Abbey for the funeral service.
Britain’s special forces, which are on constant standby for a terrorist attack, are also believed to have bolstered their numbers in the capital and elsewhere in case of any incident.
Mayor of London, Sadiq Khan, said the funeral presented an “unprecedented” security challenge.
“It’s been decades since this many world leaders were in one place,” he said. "This is unprecedented … in relation to the various things that we’re juggling.
“There could be bad people wanting to cause damage to individuals or to some of our world leaders."
King Charles III and Queen Consort Camilla returned to Buckingham Palace on Sunday to host world leaders and official overseas guests at a state event.
Prince Andrew, the Duke of York, has paid tribute to his mother, the queen. He said: "Mummy, your love for a son, your compassion, your care, your confidence I will treasure forever."
He hailed the late monarch's "knowledge and wisdom infinite, with no boundary or containment". He said: "I will miss your insights, advice and humour."
At 10am on Sunday, an online tracker said the estimated queuing time to see the queen's coffin was 14 hours — far shorter than the peak of more than 25 hours on Saturday — as the line of people tailed back to Southwark Park in Bermondsey, six kilometres from Westminster.
At 4pm people joining the queue had a 10-hour wait ahead of them.
One of the UK's biggest transport operations is also being set up, with Transport for London (TfL) preparing for about one million visitors on Monday.
About 250 extra rail services will run — including some overnight trains — and National Highways has suspended planned motorway closures in England.
There are fears the transport network will be overwhelmed on Monday afternoon if too many people visiting the capital travel home as soon as the funeral procession leaves Westminster.
Meanwhile, at 8pm on Sunday, the country will observe a one-minute silence to remember the queen, with people invited to mark the occasion privately at home, on their doorstep or street, or at community events and vigils.
There will also be a service of reflection near Falkirk, Scotland at 7.30pm, where 96 lanterns will be lowered into the pool at the foot of the Queen Elizabeth II Canal, before wreaths are placed on the water.
It will come shortly after the queen consort pays a televised tribute to the celebrated monarch, recalling her “wonderful blue eyes” and saying: “I will always remember her smile.”
Camilla will speak of how Queen Elizabeth was a “solitary woman” in a male-dominated world.
She will say: “I can't remember anyone except the queen being there.”