The Department for Digital, Culture, Media and Sport's (DCMS) online tracker shows that the expected wait time is more than 24 hours, with people queuing from Southwark Park in south-east London to pay their respects to the queen's coffin in Westminster Hall, about eight kilometres away.
Despite the warnings of chilly temperatures and the long wait, a steady stream of people followed in the footsteps of former professional footballer David Beckham a few hours earlier and joined the queue on Friday evening, many wearing coats and jumpers.
Tatie Kirst, 38, of Canada Water in south-east London, said: “Well, it's a journey right?
“I think I'm prepared, I brought my good coat, I have a stool if I need to sit, I'm getting food and water, and we're going to walk the way.
“I think there is always a question. Is it worth it? Can I make it? And hopefully, yes.
“I wanted to be part of this, pay my respect to the queen.”
The queue was earlier paused for 40 minutes when it reached capacity, and when it reopened, mourners were urged by the DCMS not to join the line until at least 4pm.
Officials stopped people from joining the queue entirely at about 11.35am at the entrance to Southwark Park due to overwhelming demand.
Downing Street said the queue system was going to plan.
James Birchall, 33, who travelled from Liverpool to pay his respects, was also queuing.
He said: “Now I just feel normal and unemotional but as I get closer and closer [to the queen's coffin], I think I'll start to become more emotional and maybe five minutes before I go in, I'll probably, even though I don't look like the type of person, I'll probably start crying.
“I absolutely loved the queen, she was great, she had been there all my life, I have always had respect for her. She was great for our country, always did her duty right until she died.
“When she died, I was overcome with emotion and I thought, I have got to come to London to see it.”
On the thousands of people queuing, he added: “I'm absolutely amazed because there is so many people, young and old — I did not think young people would come, necessarily, because they are not really in tune with monarchy, but there's so many young people here to pay their respects which I think is awesome.”
The public pay their respects to Queen Elizabeth II at Westminster — in pictures
Also queuing was Vlasta Picker, 73, of Bedford, who said: “I came here in 1977 on the silver jubilee.
“Growing up in Central Europe, monarchy was a thing of the past, history.
“I was really quite mesmerised, it was massive in 1977 and I have admired her ever since because she was a wonderful person, unique.
“To serve all her life until the end, it's something, isn't it? Unprecedented. And that's why I want to be here.”
Figures from the London Ambulance Service (LAS) show that 435 members of the public were treated along the route of the queue and surrounding areas over the past two days.
About 291 people along the route of the queue and nearby in London were given medical assistance on Wednesday, with 17 needing hospital treatment, the LAS said.
A further 144 people were treated on Thursday, with 25 people being taken to hospital.
The LAS said the majority of incidents attended were faints and collapses, resulting in head injuries.