QUEEN'S DEATH - LATEST DEVELOPMENTS
* United in grief - Charles, William and Harry walk with Queen's coffin to Westminster Hall
* Kate and Meghan put aside their differences to mourn side by side
* Thousands of mourners have started their long vigil to pay respect, with some estimates of 30-hour waiting times
* Opinion: King Charles' pen tantrums reveal a worrying truth
* NZ's one-off public holiday - all you need to know

The coffin of Queen Elizabeth II left Buckingham Palace for the last time early today (NZT), borne on a horse-drawn carriage and saluted by cannons and the tolling of Big Ben, in a solemn procession through the flag-draped, crowd-lined streets of London to Westminster Hall. There, Britain's longest-serving monarch is lying in state for the world to mourn.

Her son, King Charles III, his siblings Princess Anne, Prince Andrew and Prince Edward and sons Prince William and Prince Harry marched behind the coffin, which was topped by a wreath of white roses and her crown resting on a purple velvet pillow.

The scenes were a poignant reflection of 25 years ago, when William and Harry walked behind the coffin of their mother, the late Princess of Wales, Diana. Then, the Prince of Wales was 15 and the Duke of Sussex was 12.

The new Princess of Wales and the Duchess of Sussex followed in separate cars to today - although Kate and Meghan were side by side once they arrived at Westminster Hall, united in their mourning for the late monarch.

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The queen will lie in state for four days until her funeral Monday, with hundreds of thousands of people expected to file past. Eight pall bearers carried the oak and lead-lined coffin into Westminster Hall, placing it on a raised platform known as a catafalque.

Shortly after 5pm Wednesday (4am Thursday NZT), the first members of the public were allowed to file past the coffin. They moved in two lines, one on either side of the coffin.

Many were in tears as they approached the casket. Some doffed their hats and one curtseyed. One fell to one knee and blew a kiss.

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The military procession from Buckingham Palace was designed to underscore the Queen's seven decades as head of state as the national mourning process shifted to the grand boulevards and historic landmarks of the UK capital.

Prince William, Prince of Wales, Catherine, Princess of Wales, Prince Harry, Duke of Sussex and Meghan, Duchess of Sussex. Photo / AP

Thousands who had waited for hours along The Mall outside the palace and other locations along the route held up phones and cameras, and some wiped away tears, as the procession passed. Applause broke out as the coffin passed through Horse Guards Parade. Thousands more sat in nearby Hyde Park watching on large screens.

Britain's King Charles III, Princess Anne, Camilla, the Queen Consort, Tim Laurence, Prince Edward, and Prince William pay their respects to Queen Elizabeth II. Photo / AP

The coffin was draped in the Royal Standard and topped with the Imperial State Crown — encrusted with almost 3000 diamonds — and a bouquet of flowers and plants, including pine from the Balmoral Estate, where Elizabeth died last Friday (NZT) at the age of 96.

Two officers and 32 troops from the 1st Battalion Grenadier Guards in red uniforms and bearskin hats walked on either side of the gun carriage. The 38-minute procession ended at Westminster Hall, where Archbishop of Canterbury Justin Welby led a service attended by Charles and other royals.

King Charles walks as procession with the coffin of Queen Elizabeth II arrives at Westminster Hall from Buckingham Palace. Photo / Getty Images

"Let not your heart be troubled: ye believe in God, believe also in me. In my Father's house are many mansions: if it were not so, I would have told you," Welby read from the Book of John.

After a short service, the captain of The Queen's Company 1st Battalion Grenadier Guards, assisted by a senior sergeant, laid the royal standard of the regiment on the steps of the catafalque.

Four officers from the Household Cavalry - two from the Life Guards and two from the Blues Royals - began the first vigil at the coffin, taking their places at each corner and bowing their heads.

Thousands had queued up along the banks of the River Thames, waiting to enter the hall and pay their respects.

The crowds are the latest manifestation of the nationwide outpouring of grief and respect for the only monarch most Britons have ever known after her 70 years on the throne.

Esther Ravenor, a Kenyan who lives in the UK, said she was humbled as she watched the procession.

"I love the Queen, I love the royal family, and you know, I had to be here," she said. "She is a true role model. She loved us all, all of us. Especially someone like me, a migrant woman coming to the UK 30 years ago, I was allowed to be here and to be free and safe, so I really honour her. She was a big part of my life."

Major General Christopher Ghika, of the Household division, who organised the ceremonial aspects of the Queen's funeral, said it was "our last opportunity to do our duty for the queen, and it's our first opportunity to do it for the king, and that makes us all very proud."

Troops involved in the procession had been preparing since the queen died. So had the horses of the King's Troop Royal Horse Artillery.

Sergeant Tom Jenks said the horses were specially trained, including how to handle weeping mourners, as well as flowers and flags being tossed in front of the procession.

Heathrow Airport temporarily halted flights, saying it would "ensure silence over central London as the ceremonial procession moves from Buckingham Palace to Westminster Hall."

President Joe Biden spoke Wednesday with Charles to offer his condolences, the White House said.

Biden recalled "the Queen's kindness and hospitality" she hosted them and the first lady at Windsor Castle in June, the statement said. "He also conveyed the great admiration of the American people for the Queen, whose dignity and constancy deepened the enduring friendship and special relationship between the United States and the United Kingdom."

Crowds have lined the route of the queen's coffin whenever it has been moved in its long journey from Scotland to London.

On Tuesday night, thousands braved a typical London drizzle as the hearse, with interior lights illuminating the casket, drove slowly from an air base to Buckingham Palace.

Earlier, in Edinburgh, about 33,000 people filed silently past her coffin in 24 hours at St. Giles' Cathedral.

Hundreds of thousands are expected to visit the 900-year-old Westminster Hall, the oldest building in Parliament, before her state funeral Monday. The line snaking along the banks of the River Thames was nearly three miles long, according to a government tracker.

The hall is where Guy Fawkes and Charles I were tried, where kings and queens hosted magnificent medieval banquets, and where ceremonial addresses were presented to Queen Elizabeth II during her silver, golden and diamond jubilees.

Chris Bond, from Truro in southwest England, was among those waiting to see the queen's coffin. He also attended the lying in state of the Queen's mother in 2002.

"Obviously, it's quite difficult queuing all day long, but when you walk through those doors into Westminster Hall, that marvellous, historic building, there was a great sense of hush and one was told you take as much time as you like, and it's just amazing," he said.

"We know the queen was a good age and she served the country a long time, but we hoped this day would never come," he added.

Chris Imafidon, secured the sixth place in the queue.

"I have 1001 emotions when I see her," he said. "I want to say, God, she was an angel, because she touched many good people and did so many good things."

Crowds gather in London, warnings of 'unprecedented' queue

Mourners in London wanting to see the Queen's coffin could expect to wait in line for up to 30 hours.

The Daily Mirror reported 750,000 mourning members of the public are expected to queue, with Culture Secretary Michelle Donelan telling Tory lawmakers in a group chat: "Queues could be up to 30 hours as we are obviously expecting and planning for unprecedented demand."

The New York Post has reported Palace officials have estimated the line to pay respects will be "miles long".

The Queen's coffin arrived at Buckingham Palace on Tuesday evening (Wednesday afternoon NZT). Photo / AP

The line to see the coffin will be open 24 hours a day and the Mirror has reported there will be port-a-potties placed along the queue route – which is expected to stretch nearly 5km.

Mourners have been told they will need a wristband to enter the queue and will not be able to take large bags, food, drinks, or tributes into the palace.

Crowds began massing early along the flag-lined mall outside the palace for the procession.

They are the latest manifestation of a nationwide outpouring of grief and respect for the only monarch most Britons have ever known, who died at her beloved Balmoral summer retreat last week at age 96, ending a 70-year reign.

People stood behind metal barriers or sat on folding chairs, umbrellas at the ready, takeout coffees in hand under gray skies hours before the coffin was scheduled to leave the landmark palace.

Crowds have lined the route of the Queen's coffin whenever it has been moved in its long journey from Scotland back to London.