Queen Elizabeth II's lying-in-state won't begin until Wednesday evening, but people have already started lining up in London more than 24 hours before the first mourners will be allowed in for their chance to pay their respects to the history-making monarch.
The queen's coffin traveled from Scotland to England on Tuesday ahead of the traditional lying-in-state at the Palace of Westminster.
The public will be able to walk past the queen's coffin to pay their respects starting at 5 p.m. local time on Wednesday. People will be able to view the coffin 24 hours a day through 6:30 a.m. on Sept. 19 -- the day of the queen's funeral.
The government warned the public to expect to wait in line for "many hours, possibly overnight," and advised people to bring food and drinks to consume while waiting as well as any essential medication.
"Large crowds are expected and people are encouraged to check ahead, plan accordingly and be prepared for long wait times," the government said.
On Tuesday afternoon, about half a mile from the Palace of Westminster, a half dozen people had already started gathering at what will be the start of the line alongside the River Thames. Most had camping chairs and some had a tarpaulin to sit under. The crowd sang hymns to the queen as they got set up to wait all night in the rain -- worried that they might risk missing their chance to pay their respects to the late monarch.
Some 350,000 people are estimated to be able to get in to view the queen's coffin, the Times reported, and authorities have warned of at least 24-hour waits outside in a miles-long line.
Glyn Norris, 63, was among those getting ready to wait Tuesday. He told ABC News it was a "no-brainer" to be in line already.
"I wanted to be here to get relatively quick (laughs) into there because I hear there's around 350,000 people," he said.
Norris described Queen Elizabeth, who died on Thursday at the age of 96 after a historic 70-year reign, like a "grandmother that I've never met."
"I thought, she's reigned for 70 years -- 24 hours in the rain isn't going to hurt me," he said. "I think she's done a fantastic job, and I'm very proud to be British."
People in the line are not allowed to camp in tents, so he and others will just be in coats or sleeping bags sitting up overnight.
Norris has come prepared with a bag full of supplies for the next day and a half, including an umbrella, phone chargers, batteries, food, drinks, warm clothing and an, ahem, pee bag.
"I've got about everything in this bag that Bear Grylls would be proud of," he said.
ABC News Royal Contributor Victoria Murphy believes the ceremonies for the queen's death could be even bigger than her Platinum Jubilee in June celebrating her 70-year reign.
Some 300,000 people came in 1952 to see Queen Elizabeth's father, King George VI, lying in state, Murphy said. "That record, I think, is going to be absolutely smashed," he said.
Once mourners make it inside Westminster Hall, the coffin will rest on a raised platform and "be draped in the Royal Standard with the Orb and Sceptre placed on top," the U.K. government said.
There will be "airport-style security" at the viewing and only small bags are permitted. Among the restricted items are flowers or other tribute items.
A dedicated floral tribute area has already been established in Green Park, one of the Royal Parks of London. Park officials politely request that mourners do not bring non-floral objects, "such as teddy bears or balloons." So that means no Paddington Bears in the queen's honor.
A ceremonial procession will be held from Buckingham Palace to the Palace of Westminster ahead of the lying-in-state. Members of the public can watch the procession in viewing areas along the route or at a screening in Hyde Park.
For those not up for the long lines or otherwise unable to travel, key moments of the ceremonial procession and the lying-in-state will be broadcast on the BBC, Sky News and ITV.
ABC News' Zoe Magee contributed to this report.