LONDON (AP) — U.S. President Joe Biden paid his respects at Queen Elizabeth II’s coffin on Sunday as thousands of police, hundreds of British troops and an army of officials made final preparations for the queen’s state funeral — a spectacular display of national mourning that will also be the biggest gathering of world leaders for years.

Biden and first lady Jill Biden were among thousands of mourners — from locals and tourists to royals and world leaders — to pay their respects at Westminster Hall, where the queen is lying in state. The president made the sign of the cross and put his hand to his heart as he stood quietly near the casket in the ornate 900-year-old hall with his wife and U.S. Ambassador Jane Hartley.

Biden then signed the official condolence book and attended a reception Sunday at Buckingham Palace hosted by King Charles III. He is one of 500 world leaders and royals invited to the queen’s state funeral Monday at Westminster Abbey, along with hundreds of British charity workers.

Biden called Queen Elizabeth II “decent” and “honorable” and “all about service” as he signed the condolence book, saying his heart went out to the royal family.

“Queen Elizabeth lived her life for the people,” Jill Biden wrote in a book for spouses and ambassadors. “She served with wisdom and grace. We will never forget her warmth, kindness and the conversations we shared.”

As the dignitaries poured in, the clock was ticking down for those seeking a place in the longest queue many have ever seen to file past the queen’s coffin. The miles-long queue is expected to be closed to new arrivals later Sunday so that everyone now in the line can view the coffin before Monday morning, when it will be taken to Westminster Abbey for the queen’s funeral.

Family by family, thousands of people kept joining the line around the clock, braving chilly overnight temperatures and waits of up to 17 hours in a queue that stretched for over 5 miles (8 kilometers).

Lauren Wilson, a 36-year-old student, was in the much shorter queue for people with mobility issues. She said she wanted to experience in person the coffin lying in state.

“The world is in such a weird place and then this happened. It feels more momentous,” she said.

She worried that the pageantry surrounding Elizabeth’s death deprives the queen’s relatives of the ability to come to terms with their loss.

“The family are not allowed to grieve. I find it quite heartbreaking,” she said.

The queen’s eight grandchildren, led by heir to the throne Prince William, circled the coffin and stood with their heads bowed during a silent vigil on Saturday evening.

Among the foreign leaders in London was New Zealand Prime Minister Jacinda Ardern, who told the BBC she was humbled to represent her nation at the funeral and to witness the national outpouring of grief and respect for the late queen.

“The thing that I will take away from this period is just the beauty of the public’s response, the kindness that you see from members of the public, the patience, the camaraderie. That has been, for me, the most moving tribute of all, has been the public response of the British people,” she said.

People across the U.K. will also pause Sunday evening for a nationwide minute of silence to remember the queen, who died Sept. 8 at 96 after 70 years on the throne. Monday has been declared a public holiday, and the funeral will be broadcast to a huge television audience worldwide and screened to crowds in parks and public spaces across the country.

Police officers from around the country will be on duty as part of the biggest one-day policing operation in London’s history.

Crowds also gathered Sunday near Windsor Castle, where the queen will be laid to rest at a private family ceremony on Monday evening.

Steve Beeson came with his family of three and a bouquet of flowers he had purchased for the queen.

“She has been a constant steadying of the reins for the country through all of these really rough times, the least we can do is come and say ‘Thank you,’” he said.

Camilla, the queen consort, paid tribute to her mother-in-law in a video message, saying the monarch “carved her own role” as a “solitary woman” on a world stage dominated by men.

“I will always remember her smile. That smile is unforgettable,” said Camilla, who is married to Charles.

Ukraine’s first lady, Olena Zelenska, was also among mourners paying respects to the queen’s coffin. British royal officials said Zelenska met with Catherine, the Princess of Wales, at Buckingham Palace on Sunday afternoon. They did not release further details. The British government has been among the strongest supporters of Ukraine since it was invaded by Russia in February.

On Saturday night, it was the grandchildren’s time to mourn. William and Prince Harry, Charles’ sons, were joined by Princess Anne’s children, Zara Tindall and Peter Philips; Prince Andrew’s daughters, Princess Beatrice and Princess Eugenie; and Prince Edward’s two children — Lady Louise Windsor and James, Viscount Severn.

William stood with his head bowed at the head of the coffin and Harry at the foot. Both princes, who are military veterans, were in uniform. The crowd kept slowly, silently filing past.

“You could see that they were thinking hard about their grandmother, the queen,” said Ian Mockett, a civil engineer from Oxford in southern England. “It was good to see them all together as a set of grandchildren, given the things that have happened over the last few years.”

The lying-in-state continues until early Monday morning, when the queen’s coffin will be moved on a gun carriage pulled by 142 Royal Navy sailors to nearby Westminster Abbey for the funeral, the finale of 10 days of national mourning for Britain’s longest-reigning monarch.

After the service Monday at the abbey, the late queen’s coffin will be transported through the historic heart of London on the state gun carriage. It will then be taken in a hearse to Windsor, where the queen will be interred alongside her late husband, Prince Philip, who died last year at 99.

Sumita Tanda put down bright red roses as a huge floral tribute bloomed near Windsor Castle.

“I feel so privileged to be a local resident of Windsor,” she said. “I just wanted to pay my respects.”