Formal celebrations for the Platinum Jubilee began on Thursday with Trooping the Colour, an annual military review that has marked the sovereign’s official birthday since 1760.
The Queen made her way onto the balcony of Buckingham Palace just after 12.20pm (9.20pm AEST), resplendent in blue and using a walking stick.
Prince William dons bearskin hat as UK celebrates Platinum Jubilee
Her majesty, who first emerged alongside Prince Edward, the Duke of Kent, was set to be joined by working members of the royal family before 70 aircraft roared overheard.
The jubilee is being commemorated with a four-day holiday weekend in the UK.
Throughout the weekend, neighbourhood organisations and individuals are expected to hold thousands of street parties around the country, repeating a tradition that began with the Queen’s coronation in 1953.
The 96-year-old Queen is Britain’s longest-reigning monarch and the first to reach the milestone of seven decades on the throne.
The jubilee is giving many people — even those often indifferent to the monarchy — a chance to reflect on the state of the nation and the huge changes that have taken place during her reign.
Former prime minister John Major — one of the 14 prime ministers of the Queen’s reign — said the monarch’s stoic presence had helped steer the country over the decades.
“The Queen has represented our better selves for over 70 years,” he told the BBC.
In a written jubilee message, the Queen thanked people in Britain and across the Commonwealth involved in organising the celebrations.
“I know that many happy memories will be created at these festive occasions,” Elizabeth said.
“I continue to be inspired by the goodwill shown to me, and hope that the coming days will provide an opportunity to reflect on all that has been achieved during the last 70 years, as we look to the future with confidence and enthusiasm.”
Congratulations arrived from world leaders. French President Emmanuel Macron called Elizabeth “the golden thread that binds our two countries” and one of “very few constants” on the international stage.
“You are our friend, such a close ally, our example of service to others,” Macron told the Queen in an English-language video message.
The name of the long weekend’s first event, Trooping the Colour, refers to a regimental flag, or “colour,” that is trooped through the ranks.
Britain’s annual tradition for the Queen’s birthday is a ceremonial reenactment of the way battle flags were once shown to soldiers to make sure they would recognise a crucial rallying point if they became disoriented in combat.
The troops that take part come from the army’s household division, composed of the seven regiments that perform ceremonial duties for the queen. Their members are fully trained soldiers and often deployed overseas when not on ceremonial duty.
Each year a different unit has the honour of trooping its colour. The 1st Battalion of the Irish Guards will have the spotlight during the Platinum Jubilee.
Thousands of people, some of whom camped overnight, lined the parade route — many of them sporting Union Jack flags, party hats or plastic tiaras.
Carly Martin, who caught a late-night bus from south London with her daughter, said she had come “to make memories”.
“You’re never going to see this again in your lifetime,” she said.
“At least not in mine, maybe not in my daughter’s … 70 years — it is all I have ever known.”
The Queen is expected to appear twice on the balcony of Buckingham Palace but Prince Charles will play a key role during the event, taking the salute of passing soldiers on his mother’s behalf.
Elizabeth has had trouble getting around of late, and her courtiers have been careful to keep make things as simple for her as possible.
The Duke and Duchess of Sussex will join other royals to watch the spectacle. The couple have travelled from their home in California to take part in the celebrations.