Britain's Queen Elizabeth II poses for a photograph at Windsor Castle. Reuters
Millions of people across Britain and the world are expected to join the festivities starting on Thursday in honour of the 96-year-old, who has reigned for longer than any of her predecessors, the government said.
"Thank you to everyone who has been involved in convening communities, families, neighbours and friends to mark my Platinum Jubilee, in the United Kingdom and across the Commonwealth," Elizabeth said in a statement.
"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."
However, in a sign of the monarch's advancing years and recent "episodic mobility" issues which have led her to cancel some engagements, Elizabeth's personal involvement in the events might be somewhat limited.
Royal fans stand next a cardboard cutout of Britain's Queen Elizabeth in London, Britain. Reuters
The celebrations begin with the Trooping the Colour military parade in central London, and for the first time Elizabeth will take the salute from the 1,500 soldiers and officers from the balcony of Buckingham Palace.
Other senior royals, including son and heir Prince Charles, 73, and his eldest son Prince William, 39, will carry out other ceremonial duties on her behalf, although much attention will be focused on those who will not be present.
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, is not expected to attend.
Her grandson Prince Harry, now living in Los Angeles with his American wife Meghan, will also be absent when the royal family gathers on the palace balcony to watch a fly-past by modern and historic Royal Air Force planes after the parade.
People gather along The Mall for the Queen's Platinum Jubilee celebrations in London on Thursday. Reuters
There will also be gun salutes in London, across Britain and from Royal Navy ships at sea at midday, while in the evening beacons will be lit across the country and the Commonwealth, with the Queen leading the lighting of the Principal Platinum Jubilee Beacon at her Windsor Castle home.
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 Feb. 1952.
Polls show she remains hugely popular and respected among her subjects, with one survey this week showing eight in 10 people held a positive view of her, and another found three-quarters thought she had done a good job as Queen.
Friday will see a thanksgiving service at London's St. Paul's Cathedral, while on Saturday royal family members will attend the Epsom Derby horse race.
A police officer walks down The Mall during the Queen's Platinum Jubilee celebrations in London. Reuters
Later, there will be a concert outside Buckingham Palace, featuring the likes of rock group Queen, American R&B singer Alicia Keys, and US singer Diana Ross.
On Sunday, officials estimate more than 16,000 street parties will take place in Britain, and the British government says some 600 "Big Jubilee Lunches" will be held in 80 countries from Greenland to New Zealand.
Celebrations will conclude with a pageant through the British capital.
"The Queen is what is great in Great Britain," said Mary-Jane Willows, 69, from Cornwall, southwest England, who was camping out on the Mall boulevard, leading to Buckingham Palace, where lamposts are bedecked in Union flags.
"Without the Queen, Britain would be Britain, but she makes it great. She stands for everything that I am proud of."
Not everyone will be joining in the festivities though. Anti-monarchy campaign group Republic, which is putting up the message "Make Elizabeth the last" on billboards across Britain, said a survey showed more than half of the public were not interested in the jubilee.
But, for superfans like American Donna Werner, 70, who had travelled over from Connecticut and was also camping on the Mall, the royals and Elizabeth remain captivating.
"She’s just a role model," said Werner, who regularly comes to Britain for major royal occasions having made her first trip back in 1986. "I mean she’s just a wonderful leader and I just wanted to celebrate with her on her 70 years of being Queen."