Tributes for Prince Philip, the Duke of Edinburgh and Queen Elizabeth II's husband, have poured in from around the world for a figure who "earned the affection of generations" as UK Prime Minister Boris Johnson said.

Flags were lowered to half-mast on royal and government buildings and a notice announcing his death was pinned to the gates of Buckingham Palace on Friday.

"We give thanks, as a nation and a kingdom, for the extraordinary life and work of Prince Philip, Duke of Edinburgh," Prime Minister Boris Johnson said outside 10 Downing Street. 

Johnson said the Duke had "earned the affection of generations" at home, in the Commonwealth and across the world after first serving in the Royal Navy and then over nearly eight decades beside the Queen.

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The Duke retired from public duties in 2017 at the age of 96. He was admitted to hospital on February 16, and went home after a month during which he was treated for a pre-existing heart condition and an infection.

His death came just months before his 100th birthday in June.

Johnson said despite his many achievements, the consort would be best remembered for his "steadfast support for Her Majesty the Queen."

Former prime minister Tony Blair said the Duke "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."

Irish Prime Minister Micheal Martin led the international reaction, adding "our thoughts and prayers are with Queen Elizabeth and the people of the United Kingdom at this time."

Australia's Prime Minister Scott Morrison ordered flags to be flown at half-mast in his country after the passing of the Duke, who he said "embodied a generation that we will never see again."

The leader of the Commonwealth nation said: "The Commonwealth family joins together in sorrow and thanksgiving for the loss and life of Prince Philip. God bless from all here in Australia. He lived a long life of service to his country."

U.S. President Joe Biden paid tribute to the Duke as a selfless servant of Britain and its people.

"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," Biden said in a statement.

King Carl XVI Gustaf of Sweden called him a "great friend." He said: "Prince Philip has been a great friend of our family for many years, a relation which we have deeply valued. His service to his country will remain an inspiration to us all."

Indian Prime Minister Narendra Modi picked out his armed service background. "He had a distinguished career in the military and was at the forefront of many community service initiatives. May his soul rest in peace," he said.

Pakistan Prime Minister Imran Khan said: "Britain has lost a wise elder who was imbued with a unique spirit of public service. His role in promoting Pakistan-UK relations will always be remembered."

New Zealand Prime Minister Jacinda Ardern focused on his charity work.

"Prince Philip will be fondly remembered for the encouragement he gave to so many young New Zealanders through The Duke of Edinburgh's Hillary Award. In over 50 years of The Award in New Zealand, thousands of young people have completed life-changing challenges through the programme," she said.

EU Commission President Ursula von der Leyen said she was "saddened to hear of the passing of His Royal Highness Prince Philip." 

She tweeted: "I would like to extend my sincere sympathy to Her Majesty The Queen, the Royal Family and the people of the United Kingdom on this very sad day."

German Chancellor Angela Merkel said: "The death of Prince Philip fills me with great sorrow. His friendship to Germany, his straightforwardness and his sense of duty will not be forgotten."

French President Emmanuel Macron paid tribute to the "exemplary life" of the Duke.

"I wish to express my sincere condolences to Her Majesty Queen Elizabeth, the Royal Family and the British people upon the death of His Royal Highness The Prince Philip who lived an exemplary life defined by bravery, a sense of duty and commitment to the youth and the environment," he tweeted.

Russian President Vladimir Putin praised the Duke and wished the Queen "courage and mental fortitude in the face of a grievous and irreparable loss."

A statement from the Kremlin cited Putin as saying: "He rightfully enjoyed respect among the British and internationally."

Stephane Dujarric, spokesman for United Nations Secretary-General Antonio Guterres, said in a statement that the UN chief is saddened at the passing of Prince Philip and extends condolences to Queen Elizabeth II and the British people. 

"As royal consort, the Duke of Edinburgh capably supported the Queen in her duties as sovereign for over 60 years," the statement said. "He was known for his dedication to charitable causes as a patron of some 800 organizations, in particular those focused on the environment, industry, sport and education."