World leaders begin gathering in London from Saturday for the funeral of Queen Elizabeth II, as princes William and Harry are set to lead a vigil of her grandchildren at her coffin.

The queen's death on September 8 aged 96, after a record-breaking 70 years on the throne, has sparked an outpouring of emotion.

Members of the public braved waits that at one point were estimated to be up to 24 hours and chilly night-time temperatures to view her coffin.

Lines have snaked for miles along the River Thames since Wednesday when her coffin was brought to the UK parliament complex to lie in state.

Police are mounting Britain's biggest-ever security operation for Monday's funeral, as hundreds of dignitaries including US President Joe Biden are set to jet in.

The queen's successor, King Charles III, will meet on Saturday with the prime ministers of the Commonwealth realms -- the 14 former colonies over which he now reigns in addition to Britain.

From Australia and New Zealand to Canada, they have formally proclaimed him their new sovereign.

But republican movements are gaining ground, and efforts to keep them all in the royal fold will likely be a feature of his reign.

Charles on Friday wrapped up his maiden tour as monarch to the four nations of the United Kingdom with a visit to Wales, part of an operation dubbed "Spring Tide" to launch him in his new role.

Large crowds in Cardiff chanted "God save the king" as he shook hands with well-wishers following a multi-faith service in Llandaff Cathedral, and at Cardiff Castle.

Charles met Welsh First Minister Mark Drakeford, an avowed republican, and there was isolated booing on the streets after the new monarch was quick to declare his son William the new Prince of Wales.

But Drakeford said questions over the future of the monarchy were "a footnote to the dominant feelings of the day".

- 'Tide of emotion' -

Back in London, Charles held a 15-minute vigil with his siblings -- Princess Anne, Prince Andrew and Prince Edward -- around their mother's casket on Friday night.

They stood, eyes lowered and silent, while members of the public filed past.

Andrew -- stripped this year of his royal titles over a sex assault scandal -- was allowed to wear military uniform for the only time during the 11-day mourning period.

The Duke of York, as he is also known, flew Royal Navy helicopters during the 1982 Falklands War with Argentina.

The vigil will be repeated on Saturday evening by eight of the queen's grandchildren, including the new heir to the throne Prince William and his estranged brother Harry.

Harry -- who served two tours with the British army in Afghanistan -- has reportedly also been given special permission to wear his military uniform despite no longer being a working royal.

The move appeared to be the latest olive branch offered to Harry by the royals after he and his wife Meghan launched accusations of racism in interviews from their new home in the US.

The personal sorrow of the queen's family has been playing out in the glare of intense international attention.

But the queen's youngest son Edward said: "We have been overwhelmed by the tide of emotion that has engulfed us and the sheer number of people who have gone out of their way to express their own love, admiration and respect."

- Beckham joins queues -

The most striking manifestation of public reverence for the queen has been the vast queues of the hundreds of thousands of people wanting to bid her farewell.

Officials warned on Friday that expected queuing time had reached over 24 hours and briefly paused admission when the lines reached capacity.

Those paying their respects included former England football captain turned fashion icon David Beckham, who spent 12 hours to reach Westminster Hall.

"It's very emotional, and the silence and the feeling in the room is very hard to explain," he told reporters after filing past the coffin.

"We're all there to say thanks to Her Majesty for being kind, for being caring, for being reassuring throughout the years."

June Nayler, 76, a retired former local authority worker from Milton Keynes in central England was undaunted by the long wait she faced as she joined the back of the line in Southwark Park.

"I'm here now and going to make it all the way -- it's my duty to do it," she told AFP.

"I'm just overcome by the crowds and number of people turning out."

The public have until Monday morning to view the coffin before the queen is honoured with Britain's first state funeral in nearly six decades.

The spectacular ceremony at Westminster Abbey -- expected to be watched by millions around the globe -- will see 142 sailors pulling the gun-carriage bearing her lead-lined coffin.

It will be attended by more than 2,000 guests, but leaders from countries at loggerheads with the UK such as Russia, Belarus and Afghanistan have not been invited.

A private burial will follow at Windsor Castle after a committal service.