Mourners wishing to pay their final respects to the Queen have been warned to expect long queues.
Details have been revealed about how people can attend the lying-in-state at the Palace of Westminster.
Large crowds are expected and there are warnings those wanting to take part in the historic occasion may have to wait for hours, or even overnight.
People will face airport-style security and tight restrictions on what they can bring with them.
The lying-in-state begins at 17:00 BST on Wednesday and will last until 06:30 on Monday 19 September - the day of the Queen's funeral. It will be open 24 hours a day between those times.
The last member of the Royal Family to lie in state in the hall was the Queen Mother in 2002, when more than 200,000 people queued to view her coffin.
The Queen's funeral will be "living tradition in action", the Dean of Westminster has said.
On Monday, members of the Royal Family will follow behind the hearse as it travels to St Giles' Cathedral in Edinburgh, where the Queen's coffin will lie under vigil for 24 hours.
A service will be held and the coffin will rest at the cathedral for 24 hours for members of the public to pay their respects. The Queen's coffin is then being flown back to RAF Northolt, before travelling to Buckingham Palace.
For the lying-in-state in London, people are being warned they will need to stand for many hours - possibly overnight - with little opportunity to sit down, as the queue will be continuously moving.
Delays on public transport are expected, as well as road closures around the area.
Visitors, who will be required to go through airport-style security, are only allowed to bring one small bag with a single opening or zip per person, and there are restrictions on what can be taken in.
People are asked to respect the dignity of the event, including by remaining silent while inside the Palace of Westminster and dressing appropriately - with clothes with "political or offensive slogans" banned.
People will be asked to turn off their mobile phones or put them on silent mode and to keep noise to a minimum.
Filming, photography and the use of mobile phones or other devices will not be allowed in the security search area or the Palace of Westminster.
Those queuing are also asked not to attempt to queue on behalf of others, leave personal items unattended or put up tents.
Any prohibited items will be confiscated and not returned, it has been warned. Police may also conduct security checks along parts of the queue.
Step-free access will be available for those who need it.
Details of the route for the lying-in-state queue will be revealed on Tuesday evening.
During the lying-in-state period, the Queen's closed coffin will rest on a raised platform called a catafalque inside Westminster Hall, in the Houses of Parliament.
The coffin will be draped in in the Royal Standard with the orb and sceptre placed on top. Each corner of the platform will be guarded around the clock by a vigil of soldiers from units from the Sovereign's Bodyguard, the Household Division, or Yeoman Warders of the Tower of London.
Ahead of the lying-in-state a ceremonial procession will take place on Wednesday afternoon that will see the coffin travel from Buckingham Palace to Westminster.
Members of the public can watch the procession in person at the ceremonial viewing areas along the processional route, or at a screening site in Hyde Park.
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