US President Joe Biden and his five living predecessors joined world leaders Thursday in mourning the death of Queen Elizabeth II.

"In a world of constant change, she was a steadying presence and a source of comfort and pride for generations of Britons, including many who have never known their country without her," Biden said in a joint statement with first lady Jill Biden.

"Her legacy will loom large in the pages of British history, and in the story of our world," Biden said in a lengthy statement issued by the White House.

Out of "respect" for her memory and her seven decades as the formal head of the British state, Biden proclaimed that American flags be lowered at the White House and other federal buildings, including foreign embassies, as well as military bases and naval vessels, until sunset on the day of her internment.

Biden first met the queen in 1982 when he was a US senator from Delaware. He met with her at Windsor Castle in June 2021 on his first overseas trip as president. At the time, Biden told reporters that the monarch "reminded me of my mother in terms of the look of her and just the generosity".

During her 70-year reign, Queen Elizabeth met with every US president (with the exception of Lyndon Johnson). She met with American leaders before she even became queen. Then-Princess Elizabeth met with President Harry Truman in 1951, a year before she ascended to the throne.

Elizabeth and Prince Phillip met with the Truman family at Blair House that year during a visit to Washington.

Biden predecessor Donald Trump, who met with the queen twice during his one-term presidency, posted several messages on his social media web site Truth Social.

The former president said : "Melania and I will always cherish our time together with the Queen, and never forget Her Majesty's generous friendship, great wisdom, and wonderful sense of humor. What a grand and beautiful lady she was — there was nobody like her!"

Barack Obama, who met with the queen four times during his two terms as president, said that he and former first lady Michelle Obama were "lucky enough to come to know Her Majesty, and she meant a great deal to us".

"Back when we were just beginning to navigate life as president and first lady, she welcomed us to the world stage with open arms and extraordinary generosity. Time and again, we were struck by her warmth, the way she put people at ease, and how she brought her considerable humor and charm to moments of great pomp and circumstance," Obama added.

Obama said she made her role as queen "her own'' — "with a reign "defined by grace, elegance, and a tireless work ethic, defying the odds and expectations placed on women of her generation''.

Former presidents George W. Bush, Bill Clinton and Jimmy Carter also released statements.

In a statement, Bush said she "ably led England through dark moments with her confidence in her people and her vision for a brighter tomorrow".

"She was a woman of great intellect, charm, and wit," Bush said. "Spending time at Buckingham Palace, and having tea with Her Majesty — and her Corgis — is among our fondest memories of the presidency.''

Clinton in a statement said that he and his wife, Hillary Clinton, "join with people across the UK and the Commonwealth, and all around the world, in giving thanks for her extraordinary life".

Clinton said they "will always be grateful for the kindness she showed us through the years, particularly during our visits to Buckingham Palace in 1995 and 2000, and for all she did to deepen the Special Relationship".

Describing her reign as "remarkable", Clinton said Queen Elizabeth "led Britain through great transformations with unfailing grace, dignity, and genuine care for the welfare of all its people".

"In sunshine or storm, she was a source of stability, serenity, and strength," he added.

"Her dignity, graciousness, and sense of duty have been an inspiration, and we join the millions around the world in mourning a remarkable leader," Carter said in a statement.

The Jimmy Carter Library and Museum posted a photo on Twitter of the queen and Carter together in London in 1977.

Other American politicians from Congress to state houses, business leaders, celebrities and ordinary Americans reacted to her passing on social media.

Many Kentuckians remembered Queen Elizabeth and her many visits to the state. The queen loved horse racing and she attended America's greatest horse race, the Kentucky Derby, in 2007 while visiting the heart of US racing in Kentucky bluegrass country. Her five visits were from 1984 to 2007, with the vast majority coming in the late '80s and early '90s.

Microsoft co-founder Bill Gates tweeted that he was "very honored" to have met Queen Elizabeth and "very sad to hear of her passing". The Queen bestowed Gates with an honorary knighthood in 2005 at Buckingham Palace in London.

Philanthropist and Gates Foundation founder Melinda French Gates said in a LinkedIn post that Elizabeth's reign was "without equal".

"I will cherish the kindnesses that Queen Elizabeth II extended to our family and the remarkable leadership, resilience, and example she showed us all," she added.

"There is nothing more noble than to devote your life to the service of others," Apple CEO Tim Cook said. "We stand with the people of the UK and Commonwealth in honoring the life and dedication to duty of her Majesty Queen Elizabeth II. May she rest in peace."

Amazon founder Jeff Bezos: "I can think of no one who better personified duty. My deepest condolences to all the Brits mourning her passing today.''

Singer and actress Bette Midler remembered the Queen on Twitter, writing, "We will never see her like again. She was steadfast, staunch, and dedicated until the very end. 70 years of duty. Unbelievable."

Actor Sylvester Stallone took to Instagram to share a photo from a time that he greeted Queen Elizabeth in person. The Rocky star wrote in his tribute, "May this GREAT QUEEN rest in peace. The world will never see the likes of her again."

"Sad to hear about the passing of Queen Elizabeth II. She was a constant for us all. Respected around the world. May she rest in peace,'' said singer and actress Barbra Streisand wrote on social media.