King Charles III will lead a procession carrying his mother's coffin through London, where hundreds of thousands of mourners will pay their respects.
Queen Elizabeth's body will be transported on a horse-drawn gun carriage from Buckingham Palace to Westminster Hall on Wednesday, six days after her death in Scotland. She will remain there for four days until her funeral on Monday.
The king and other senior royals are scheduled to walk silently behind the hearse as it travels through the streets of the capital, followed by a vigil in the 12th-century hall within the Westminster parliament complex.
The public will be let in from 5:00 pm (1600 GMT), with mourners already advised they would face an endurance test in round-the-clock lineups that might snake back up to eight km.
"It's going to be emotional and I don't know how I'll feel going in there as the first one," said Vanessa Nanthakumaran, a 56-year-old Sri Lankan administrative assistant who took the front of the line on Monday evening.
"It's our duty to say thank you. It's going to be prayers from the heart. It's going to be very sombre, quiet and overwhelming."
According to a spokesperson for Prime Minister Liz Truss, strict procedures and airport-style security measures have been implemented, and "far more" people are expected than the 200,000 who filed past the coffin of the queen's mother when she died in 2002.
The administration has recommended individuals wear "suitable clothing" and bring portable battery packs to keep their mobile phones charged, indicating that some individuals will have to wait overnight to view the casket.
Even inexpensive hotel rooms in the capital are going for $350 per night, while transport managers and police are under pressure to keep the city moving and secure during extraordinary conditions.
Mark Rowley, the recently appointed chief of the London police force, told Sky News on Tuesday, "It's a massive challenge for the Metropolitan Police and for me personally, but we have been preparing for many, many years,"
The journey bringing the late monarch's body from Edinburgh to London was followed by slightly more than five million people, making it the most followed flight ever.
According to the flight tracking website Flightradar24, a total of 4.79 million people watched the flight live online, with an additional 0.2 million watching on its YouTube channel.
"A piece of history"
The remains of the late 96-year-old monarch, who died "peacefully" at her Balmoral estate in Scotland last Thursday, were carried from the Scottish capital Edinburgh to London by RAF aircraft on Tuesday evening.
The procession on Wednesday will resemble the one that took place in Edinburgh on Monday when her casket was driven through the city's quiet streets to St. Giles' Cathedral.
According to the Scottish government, almost 33,000 individuals passed by the casket between midnight and Tuesday afternoon.
"Scotland has now bid our Queen of Scots a fond farewell," said First Minister Nicola Sturgeon. "We will never see her like again."
Charles began his tour of the four nations of the United Kingdom on Tuesday by visiting Northern Ireland for the first time as monarch, following his visits to Scotland and England.
On Friday, a trip to Wales is expected.
The 73-year-old new head of state has received widespread acclaim from the British media for his polite and often sympathetic response to the loss of his mother, which has resulted in a rare moment of national unity in Britain.
Since the loss of his ex-wife Diana in a 1997 car accident, his popularity has risen, and his ratings have increased in recent days, according to a poll released on Tuesday.
The funeral of the queen will be held at Westminster Abbey in front of 2,000 VIP visitors, and the day has been declared a national holiday in Britain.
Hundreds of world leaders and royals are expected to attend, but Russia, Belarus, Myanmar, and North Korea have not been asked to send delegations.
US Vice President Joe Biden, French President Emmanuel Macron, and Canadian Prime Minister Justin Trudeau have all confirmed their attendance.