Soon after the announcement, people began to line up outside Buckingham Palace to see the official death notice that had been attached to the gate. The flag at the palace, the queen's residence in London, was lowered to half-staff.
British Prime Minister Boris Johnson said Philip "earned the affection of generations here in Britain, across the Commonwealth and around the world.''
"Like the expert carriage driver that he was, he helped to steer the royal family and the monarchy so that it remains an institution indisputably vital to the balance and happiness of our national life,'' Johnson said.
Keir Starmer, leader of the opposition Labour Party, was among the first to offer his condolences, noting Philip's long record of public service, first as as a naval officer during World War II then during more than 70 years of marriage to the queen.
"He will be remembered most of all for his extraordinary commitment and devotion to The Queen," Starmer said in a statement.
"For more than seven decades, he has been at her side. Their marriage has been a symbol of strength, stability and hope, even as the world around them changed - most recently during the pandemic. It was a partnership that inspired millions in Britain and beyond."
World leaders also expressed their sadness. Former U.S. President George Bush and his wife, Laura, offered condolences to the monarch and the entire royal family.
"He represented the United Kingdom with dignity and brought boundless strength and support to the sovereign,'' Bush said in a statement. "Laura and I are fortunate to have enjoyed the charm and wit of his company, and we know how much he will be missed.''
More reaction to the death of Prince Philip
Prince Harry and Meghan Markle
Prince Harry and Meghan Markle shared a tribute on their Archewell website in "loving memory" of Harry's grandfather.
The short message in honor of the late Duke of Edinburgh reads: "Thank you for your service...You will be greatly missed."
U.S. President Joe Biden
"On behalf of all the people of the United States, we send our deepest condolences to Her Majesty Queen Elizabeth II, the entire Royal Family, and all the people of the United Kingdom on the death of His Royal Highness Prince Philip, the Duke of Edinburgh. Over the course of his 99-year life, he saw our world change dramatically and repeatedly. From his service during World War II, to his 73 years alongside the Queen, and his entire life in the public eye -- Prince Philip gladly dedicated himself to the people of the UK, the Commonwealth, and to his family. The impact of his decades of devoted public service is evident in the worthy causes he lifted up as patron, in the environmental efforts he championed, in the members of the Armed Forces that he supported, in the young people he inspired, and so much more. His legacy will live on not only through his family, but in all the charitable endeavors he shaped.
Jill and I are keeping the Queen and to Prince Philip's children, grandchildren, and great-grandchildren in our hearts during this time."
Former U.S. President Barack Obama
"As the world mourns his loss, we send our warmest wishes and deepest sympathies to the Queen, their children, grandchildren, and great-grandchildren; and everyone who knew and loved this remarkable man."
"At the Queen's side or trailing the customary two steps behind, Prince Philip showed the world what it meant to be a supportive husband to a powerful woman. Yet he also found a way to lead without demanding the spotlight - serving in combat in World War II, commanding a frigate in the Royal Navy, and tirelessly touring the world to champion British industry and excellence. Through his extraordinary example, he proved that true partnership has room for both ambition and selflessness - all in service of something greater."
Former U.S. President George W. Bush
Former U.S. President George W. Bush has praised Prince Philip's devotion to worthy causes and to others in a statement issued on behalf of himself and his wife, Laura.
"He represented the United Kingdom with dignity and brought boundless strength and support to the sovereign. Laura and I are fortunate to have enjoyed the charm and wit of his company, and we know how much he will be missed," Bush said.
He added he and his wife offer heartfelt condolences to Queen Elizabeth II and the rest of Philip's family.
Former Prime Minister Tony Blair
Former Prime Minister Tony Blair has expressed his condolences on the death of Prince Philip, praising his role as royal consort as well as his charitable works.
Blair described Philip, also known as the Duke of Edinburgh, as a man who was way ahead of his time in fighting for the protection of the environment, reconciliation among religious faiths and in the creation of programs to help young people.
"Our whole nation will be united in sadness at the passing of Prince Philip,'' Blair said in a statement. "He will naturally be most recognized as a remarkable and steadfast support to the Queen over so many years. However, he should also be remembered and celebrated in his own right as a man of foresight, determination and courage."
France's Europe minister Clement Beaune
France's Europe minister, Clement Beaune tweeted, "Prince Philip was a grand figure of the century for the United Kingdom," following his death at age 99.
"Thoughts and friendship toward the British people," Beaune added.
News of Philip's death is trending in France but the immediate reaction was muted in this staunchly republican country.