Workmen set up barriers and thousands of police were mobilized as London geared up Tuesday for its grand farewell to Queen Elizabeth II.

The late monarch's coffin arrived in the British capital from Scotland, where she died last Thursday, before hundreds of thousands are expected to pay their respects as it lies in state.

"I've never seen something like it," security guard Rumesh told AFP near parliament, where the casket will rest.

"You can feel it's coming and that it's going to be huge."

Queues are set to stretch for miles along the River Thames as British media has speculated some 750,000 mourners will wait patiently to file past the queen in the four days ahead of her funeral on 19 September.

By Tuesday morning only a small group of the hardiest royal fans — surrounded by dozens of journalists — had set up camp at the front of the line across from the Houses of Parliament.

"From tomorrow morning onwards, the queue is going to be insane," said Rumesh.

"It's the calm before the storm."

'Funeral of century'

The authorities have already set in motion a well-prepared plan called London Bridge that had been ready to go for years for a grandiose period of national mourning and state funeral once the queen died.

Newly appointed London police boss Mark Rowley has described the upcoming days as a "massive challenge" but insisted the force had been preparing for "many, many years".

Thousands of police officers have been mobilized as some 500 leaders, including US President Joe Biden, are set to descend on the capital ahead of what is being dubbed "the funeral of the century" next Monday.

Tight airport-style security has been put in place for those hoping to see the queen's coffin as it lies in state.

A system of wrist bracelets is in place for those wanting to use the dozens of portable toilets installed along the Thames and keep their place in line.

The streets will not be the only thing crowded: Hotels around the city center are already booked up despite steep price hikes.

London's transport authorities have warned commuters of inevitable disruptions and pubs are bracing for busy times.

"We know for sure it's going to be super busy," said Mantas Butkus, who works in a pub near Westminster.

He said that extra staff had been drummed up for the days to come.

"It's the first time we have to deal with something like that, so we can't really know what to expect," he said.

'Curious to see it'

Given the mass of people expected, Joseph Afrane had already abandoned the idea of seeing the coffin in Westminster.

Instead he has been waiting since Sunday near Buckingham Palace to catch a glimpse of the hearse bringing the casket from the airport.

"It's a safer bet," he said.

"It's going to be chaos at Westminster and, you know, even if it's sad, the atmosphere is actually quite nice here."

In front of the royal residence some of the shock and grief felt in the first hours after the queen's death has subsided.

While some red-eyed visitors were still laying flowers, others walked around in a more jovial mood taking selfies in front of the tributes.

"Basically, I'm here precisely to be here. To be part of all of it. It's living history and I really wanted to come and see," said Alice Colley, 27.

"There is sadness, obviously, but also some kind of excitement. People just want to be here, they're curious to see it because we know we won't live through this again anytime soon."