US President Joe Biden paid tribute Thursday to the late Queen Elizabeth II as a "stateswoman of unmatched dignity," and said he looked forward to working with her son King Charles, noting their already "close friendship."

US President Joe Biden signs the condolence book at the British Embassy in Washington to pay his respects following the death of Britain’s Queen Elizabeth II in Washington, DC on September 8, 2022. (Photo: AFP)

Biden ordered flags at the White House and other federal buildings to be lowered to half-staff, and also visited the British embassy in Washington to sign a condolence book for the queen.

"Queen Elizabeth II was a stateswoman of unmatched dignity and constancy who deepened the bedrock alliance between the United Kingdom and the United States," Biden and First Lady Jill Biden said in a statement. "She helped make our relationship special."

At the embassy, Biden told staff the late queen was "a great lady" and that he was "so delighted I got to meet her."

Biden, 79, noted deep ties between the monarch and the United States, a former British colony.

"She stood in solidarity with the United States during our darkest days after 9/11, when she poignantly reminded us that 'Grief is the price we pay for love,'" Biden said in his statement.

The five former living US presidents -- Jimmy Carter, Bill Clinton, George W. Bush, Barack Obama, and Donald Trump -- together with their wives all issued statements Thursday, paying tribute to the late monarch.

Setting aside their political divisions, now as deep as ever in America, the former US leaders were unanimous in their respect for the queen, praising her historic legacy as well as her personal traits.

Obama hailed "a reign defined by grace, elegance, and a tireless work ethic, defying the odds and expectations placed on women of her generation."