Tens of thousands of royal supporters waving flags lined the streets of London for a military parade at the start of the four-day Platinum Jubilee. Millions of people across Britain and the world were expected to watch the festivities, join street parties and light beacons in honour of the 96-year-old Queen.
Elizabeth, holding a walking stick and wearing a dusky dove blue outfit that she also wore for an official Jubilee photograph, was joined by her son and heir Prince Charles, 73, and other senior royals on the balcony of Buckingham Palace.
While the family waved to the crowds and enjoyed a Royal Air force fly-past, Louis - Prince William's 4-year-old son - covered his ears and howled as the planes roared overhead.
Elizabeth has been on the throne for longer than any of her predecessors, and is the third-longest reigning monarch ever of a sovereign state. Opinion polls show she remains hugely popular and respected among British people.
World leaders including US President Joe Biden, France's Emmanuel Macron, Pope Francis and former British prime ministers were among those sending messages of goodwill.
The celebrations began with the Trooping the Colour, a military parade held annually to mark the Queen's official birthday, where 1,500 soldiers marched to military music in ceremonial uniforms of scarlet tunics and bearskin hats.
Later the crowds moved to the Mall, the grand boulevard running up to Buckingham Palace, where in brilliant sunshine they cheered and waved Union flags while a display of modern and historic planes took place overhead.
Thursday marks not only the start of the Jubilee, but also the 69th anniversary of the coronation of Elizabeth, who became Queen on the death of her father George VI in February 1952.
Her involvement in this year's celebrations will be somewhat limited compared with previous major events. In recent months the Queen has cut back public appearances due to what Buckingham Palace calls "episodic mobility issues". In May, she missed the opening of parliament for the first time in almost six decades.
Senior royals, including Charles, and his eldest son William, 39, are carrying out some ceremonial duties on the Queen's behalf.
Some royal family members were absent on Thursday, including the Queen's second son Prince Andrew, 62, who settled a US lawsuit in February in which he was accused of sexually abusing a woman when she was underage. Andrew denied the accusation.
The palace announced later that Andrew had tested positive for COVID-19 and would not attend a service of Thanksgiving on Friday.
Prince Harry, now living in Los Angeles with his American wife Meghan after stepping down from royal duties, watched the parade but was absent from the palace balcony, with only "working" members of the family present.
There were artillery gun salutes in London, across the United Kingdom and from Royal Navy ships at sea.
"It was lovely, everything we hoped it would be. We're a bit older now, so we were here for the 25th and then the 50th (jubilee). But this was the best one," said nurse Ian Higgins, 62, who was watching the events in central London.
In the evening beacons will be lit across the country and the Commonwealth, with the Queen set to lead with the lighting of the Principal Platinum Jubilee Beacon at her Windsor Castle home.
The government announced two public holidays to mark the celebration, which is the first major public gathering since the pandemic and a welcome distraction for many at a time of growing economic hardship.
Among the tributes pouring in from around the world was a video message from former U.S. president Barack Obama that was broadcast on the BBC.
"Your life has been a gift, not just for the United Kingdom, but for the world. And it is with gratitude for your leadership and the kindness that you've shown me and my family that I say, may the light of your crown continue to reign supreme," he said.
A number of people caused a brief disturbance by running out in front of marching soldiers on the Mall boulevard before they were dragged away by police. Several were arrested.
