Mourners view the coffin of late Queen Elizabeth

People from all walks of life, from young and old, including police officers and babies being carried by their parents stopped by the coffin to bow their heads, while others wiped away tears.

Many people waited for hours for a chance to see the Queen's flag-draped coffin, which was in the centre of parliament's Westminster Hall on a purple catafalque positioned on a red platform.

It was topped with the Imperial State Crown placed on a cushion, alongside a wreath of flowers.

Government officials said they could not put a precise figure on how many would want to file past the queen's coffin, but around 750,000 people were expected. At 1645 GMT, the government said the queue was around 2.6 miles long.

There will be a constant stream of mourners, 24 hours a day, during the four days of lying in the state that lasts until the morning of the funeral.

The queen, Britain's longest-reigning monarch, died on September 8 aged 96 and has sat on the throne for over 70 years.

Her coffin was brought to Westminster Hall earlier on Wednesday from Buckingham Palace.

King Charles, his sons Princes William and Harry and other senior royals joined a solemn procession taking Queen Elizabeth's coffin as the late monarch made her final journey from Buckingham Palace. 

Huge crowds gathered in central London to witness the queen being taken from the palace to parliament as artillery guns fired salutes and Big Ben tolled, the latest in a series of poignant ceremonies as the nation mourns the queen. 

Lying on a gun carriage, covered by the Royal Standard flag and with the Imperial State Crown placed on a cushion alongside a wreath of flowers, the coffin bearing Elizabeth's body was taken in a slow, sombre procession from her London home to Westminster Hall. There it will lie in state for four days.

Walking directly behind where Charles and his siblings, Anne, Andrew and Edward.

In a group that followed were Charles's sons Princes William and Harry, a doleful scene reminiscent of when, as boys 25 years ago, they followed the casket of their mother Princess Diana when it was taken on a similar procession through central London.

It was also a symbolic show of unity as William, 40, now the Prince of Wales, and Harry, 37, the Duke of Sussex, are said to barely be on speaking terms after a bitter falling out in the last couple of years.

Just after 5 p.m. (1600gmt), the public began to file past the coffin.

“She's been immortal, I think. And it's hard to believe she's gone,” said Naomi Gordon.

Her friend Nicole Balint added: “There is a lovely atmosphere in the crowd and we've made friends with people next to us. And I think we're going to get in there pretty quickly, much quicker than I thought."

One woman who had the chance to see the coffin lying in the state described the experience as a "personal moment of goodbye".

"Because it was my moment, it was my monarch... that's what matters. You know you can write letters of condolence which I'm sure many of us will do. But it was a personal moment of goodbye," said Paula Nicklinson.

"Once you are in Westminster Hall, the harsh, the quiet, the peace, then your heart takes over. And you know, you've come to say thank you and goodbye," she added.

The government has warned the queue could eventually stretch for up to 10 miles (16 kilometres) along the southern bank of the River Thames, winding past landmarks such as the giant London Eye Ferris wheel and the reconstruction of Shakespeare's Globe theatre. 

“She meant everything because she had been Queen all of our lives,” said Ruth Reed, who came to give respect to the queen.

“I was born when the Queen came to the throne… So yeah, she's been my queen for all of my life,” Reed added.

“It is so important to be able to pay our respects, to afford her the true recognition for an extraordinarily reign and to have that moment of quiet reflection,” Lord Lieutenant of Buckinghamshire, Countess (Elizabeth) Howe said.

People started waiting in line late on Tuesday, sleeping on the streets in the rain, to be one of the first to file past the coffin, and there was already a queue over two miles long.

Monica from the Philippines, 61, said the wait was worth it.

“It was very solemn. I think everybody shed a tear,” she added.

Elizabeth's coffin was flown back to London late on Tuesday from Scotland, where it had been since her death at her Scottish summer holiday home Balmoral Castle.