The queue to see the Queen lying in state at Westminster Hall is at capacity and entry will be paused for six hours, the government has said.
The line is now about five miles (8km) long, stretching to Southwark Park in south-east London.
But there was confusion as security staff at the park said the queue would be reopened every now and then.
Thousands have paid their respects to the Queen, who is lying in state at Westminster until 06:30 BST on Monday.
The Department for Culture, Media and Sport said at 09:08 on Friday that Southwark Park, where the queue officially ends, had “reached capacity”.
Entry would be “paused for at least six hours”, it said. “Do not attempt to join the queue until it reopens.”
A separate queue for people with accessibility needs is also at capacity, the department said.
At Southwark Park, some of those initially turned away said they had travelled hundreds of miles and were on their second attempts to access the queue.
In a moment of confusion, stewards at the park appeared to allow about 100 people into the park after the pause was announced.
Jane Sebutinde said she was on her way when she heard the queue would be paused. “Currently with my health I can’t queue for 14 hours, I thought it would be four hours,” she said.
For many of those currently in the main queue, latest estimates suggest they will not enter Westminster Hall until after midnight.
The Met Office advised those in the queue to be prepared for “cool evenings” with overnight temperatures expected to be as low as 8C (46F).
Among those waiting to pay their respects to Her Majesty was former England footballer David Beckham, who was seen queuing in Victoria Tower Gardens.
The queue follows the south bank of the River Thames from the Palace of Westminster, through Lambeth, Southwark, and into Bermondsey.
Meanwhile, a row has broken out over who is allowed to skip the queue to pay their respects to the late Queen after it emerged MPs and Lords had special access.
The announcement of the queue’s pause came shortly after it was confirmed Queen Elizabeth II’s grandchildren would hold a 15-minute vigil at Westminster Hall on Saturday evening.
The Prince of Wales and the Duke of Sussex will observe the vigil alongside six of their cousins. The royal brothers will both wear military attire for the occasion, after a request from their father, King Charles.
The King and his siblings, the Princess Royal, the Duke of York and the Earl of Wessex, will hold a similar vigil on Friday evening.
The former Prince of Wales and Camilla, the new Queen Consort, attended a prayer and reflection service for the Queen at Cardiff’s Llandaff Cathedral.
Later, they will greet members of the public at Cardiff Castle.
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