In tribute to the duke, Westminster Abbey began tolling its tenor bell once every 60 seconds at 18:00 BST. It rang out 99 times to honour each year of his life.
Earlier, the flag at Buckingham Palace was lowered to half-mast and a notice was posted on the gates to mark the duke’s death.
People placed floral tributes outside the palace, while hundreds visited Windsor Castle to pay their respects.
However, the government urged the public not to gather or leave tributes at royal residences amid the coronavirus pandemic.
The Royal Family has asked people to consider making a donation to a charity instead of leaving flowers in memory of the duke, and an online book of condolence has been launched on the official royal website, external for those who wish to send messages.
A message on the website of the Duke and Duchess of Sussex’s non-profit organisation Archewell paid tribute to the “loving memory” of the Duke of Edinburgh, saying: “Thank you for your service… you will be greatly missed.”
From midday on Saturday, a 41-gun salute will take place for Prince Philip in cities including London, Edinburgh, Cardiff and Belfast, as well as in Gibraltar and at sea from Royal Navy warships, the Ministry of Defence said. They will be broadcast online and on television for the public to watch from home.
The BBC’s royal correspondent Nicholas Witchell said it was “a moment of sadness” for the country and “most particularly, for the Queen losing her husband of 73 years – a bigger span of years than most of us can imagine”.
He said Prince Philip had made “a huge contribution to the success of the Queen’s reign”, describing the duke as “utterly loyal in his belief in the importance of the role that the Queen was fulfilling – and in his duty to support her”.
“It was the importance of the solidity of that relationship, of their marriage, that was so crucial to the success of her reign,” he added.