At 8pm, the country will observe the 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.
Big Ben will toll to start the beginning of the national moment of reflection and the bell will be struck once more at 8.01pm as it ends.
Andrew is the latest royal to pay tribute to his mother, hailing her “knowledge and wisdom infinite, with no boundary or containment”, adding: “I will miss your insights, advice and humour”.
He described the Queen as “Mummy, Mother, Your Majesty, three in one” and said it had been an “honour and privilege” to serve her.
It came as the public continued queuing for the final day of the lying in state in Westminster Hall, where the late monarch’s coffin will remain until 6.30am on Monday.
People have been warned not to set off from their homes to join the queue as it is due to close later on Sunday.
The Department for Culture, Media and Sport (DCMS) said: “A decision will be taken today on when entry to the queue for Her Majesty The Queen’s Lying-in-State will close as it reaches final capacity.
“Queue times are already 13.5 hours and may increase.
“To avoid disappointment please do not set off to join the queue.”
Waiting times were far shorter than the peak of more than 25 hours that was seen in the early hours of Saturday morning.
However, St John Ambulance said in the early hours of the morning some 98 people needed medical support, nine of whom were taken to hospital.
Elsewhere, world leaders continued arriving in the UK for Monday’s funeral service at Westminster Abbey.
Irish premier Micheal Martin entered Downing Street for a “warm” meeting with Liz Truss at 10am to discuss “many issues in the context of the British-Irish relationship”, before leaving just under an hour later.
The Taoiseach told reporters in London: “I appreciate the opportunity to be here at the funeral accompanying the president to pay our tribute to Queen Elizabeth’s dedicated service to the people of the United Kingdom and of course, her contribution to reconciliation on these islands and particularly in terms of the relationship between Britain and Ireland.”
Canadian prime minister Justin Trudeau also met with the Prime Minister a few hours later.
The PM kicked off her meetings with world leaders on Saturday, speaking to her counterparts from New Zealand and Australia.
Ms Truss will also have an audience with King Charles III before attending his reception for visiting heads of state at Buckingham Palace.
The King and Queen Consort are to host world leaders and official overseas guests at the palace, in what the King’s spokesman described as an “official state event”.
Camilla will pay a televised tribute to the late monarch, recalling her “wonderful blue eyes” and saying: “I will always remember her smile.”
In pre-recorded words on the BBC, she will speak of how Queen Elizabeth II was a “solitary woman” in a male-dominated world.
She will add: “I can’t remember anyone except the Queen being there.”
There will also be a service of reflection near Falkirk, Scotland at 7.30pm.
It will see 96 lanterns, one for each year of the late monarch’s life, lowered into the pool of reflection at the foot of the Queen Elizabeth II Canal, before wreaths are placed into the water.
The DCMS has said the Queen’s funeral will be shown on giant screens in various locations across the UK, from London’s Hyde Park to Coleraine Town Hall in Northern Ireland.
Around 125 cinemas will also be screening the event, along with Sky News, ITV and the BBC for people watching from home.
On Saturday evening, the Queen’s eight grandchildren together staged a heart-rending evening vigil around their beloved Granny’s coffin.