The Queen has visited a school in Norfolk as she marks the 60th anniversary of her accession to the throne.
Earlier she said she was dedicating herself "anew to your service" and that she was "deeply moved" by support for the Diamond Jubilee.
The Queen was met by crowds at King's Lynn Town Hall before going to Dersingham Infant and Nursery School.
Gun salutes were held around the UK, including in London and Edinburgh.
The main celebrations for her anniversary will be in June.
The Queen, 85, usually spends Accession Day - the day her father, George VI, died in 1952 - privately but this year has the two engagements in Norfolk.
Two official photographs were released and a 41-gun salute was held in Hyde Park, London, followed by a 62-gun salute at the Tower of London.
There was also a 21-gun Royal Salute at Edinburgh Castle at noon.
At the end of the Queen's tour, pupils at Dersingham Infants gathered in the school hall for a musical performance where she was the guest of honour.
Head teacher Gayle Platt said the visit had been "incredible" and she felt "very, very privileged".
"We've made the day a big occasion for the children that will continue now the Queen's gone," she said.
During her reign, Queen Elizabeth II has seen 11 UK prime ministers come and go, with David Cameron her 12th.
Mr Cameron praised the "magnificent service" given by the Queen and called her a "source of wisdom and continuity".
"With experience, dignity and quiet authority she has guided and united our nation and the Commonwealth over six varied decades," he said.
Among the crowds waiting for the Queen in King's Lynn was Laura Skrzynski, who travelled from London.
She said: "I love that the monarchy is above politics and feel that the Queen represents that best of all.
"She stands for integrity and respect and I am inspired by her faith. She has been a constant through all our lives."
Members of the Church of England General Synod, its national assembly, stood to sing the first verse of the National Anthem before giving unanimous approval to a loyal address marking the Queen's 60 years on the throne.
Archbishop of Canterbury Dr Rowan Williams said the Queen's position was "not a secular office but a Christian one".
Paying tribute to the monarch and her father, George VI, he told the Church's national assembly: "The Diamond Jubilee celebrates much more than the length of Her Majesty's reign, though that is remarkable in itself. She has been our Queen for as long as most of us can remember.
"None of us can imagine what it would be like to hold the same office for 60 years - Her Majesty's life is one in which the privilege accorded by birth has been richly earned by generous service."
Meanwhile, former prime minister Sir John Major has formally launched the Queen Elizabeth Diamond Jubilee Trust to help those in need across the Commonwealth.
He will chair the grant-making body, which will focus on areas such as fighting curable diseases and the promotion of education and culture.
A set of six 1st class definitive stamps, all of which feature official portraits of the Queen, are also being issued to mark the monarch's milestone.
Moya Greene, Royal Mail's chief executive, said: "The Queen's image is one of the most recognisable in the world and we are delighted to bring these iconic images together to mark the 60th anniversary of the Queen's accession."
The Diamond Jubilee Miniature Sheet marks the first occasion on which official images of the monarch, sourced from stamps, coins and banknotes, have been brought together for a stamp issue.
The Queen's 60 years as monarch are set to be marked by a series of regional, national and international events during 2012, culminating in a four-day long UK Bank Holiday weekend in June.
undefinedinclude the Queen leading a flotilla of a thousand boats along the Thames and a chain of beacons being lit across the country.
There will be a service of thanksgiving at St Paul's Cathedral in June and a formal carriage procession by the Queen.
The Queen and the Duke of Edinburgh also intend to travel as widely as possible across the UK.
Other members of the Royal Family will visit the 15 other countries where the Queen is head of state, as well as some other Commonwealth countries.
In her message to mark the anniversary, the Queen said: "I am writing to thank you for the wonderful support and encouragement that you have given to me and Prince Philip over these years and to tell you how deeply moved we have been to receive so many kind messages about the Diamond Jubilee.
"In this special year, as I dedicate myself anew to your service, I hope we will all be reminded of the power of togetherness and the convening strength of family, friendship and good neighbourliness, examples of which I have been fortunate to see throughout my reign and which my family and I look forward to seeing in many forms as we travel throughout the United Kingdom and the wider Commonwealth."