By Agence France-Presse
Horse-drawn guns fired 41 times in Hyde Park and 62 times at the Tower of London, while at Windsor Castle, the band played "Happy Birthday" during the changing of the guard.
In the evening, the monarch and her family were due to attend a concert with performers from around the Commonwealth, the 53-nation grouping which held its summit in London this week.
Australia's Kylie, Canadian pop chart-topper Shawn Mendes, South African all-male choir Ladysmith Black Mambazo and US-Jamaican reggae star Shaggy were to join British stars including Jones, Craig David and Sting.
The queen usually celebrates her birthday in private, saving the pomp for her official birthday in June.
The concert at the Royal Albert Hall will raise money for a new youth charity, The Queen's Commonwealth Trust.
The monarch's grandson Prince Harry, who will marry US actress Meghan Markle at Windsor on May 19, is the trust's new president and was due to give a speech at the concert.
The queen has been the symbolic head of the Commonwealth since her father king George VI's death in 1952, but its leaders agreed on Friday that her son and heir Prince Charles should succeed her.
The summit was overshadowed by a row over Britain's treatment of Caribbean immigrants, while Charles himself also came under scrutiny.
A non-white writer, Anita Sethi, claimed he joked about whether she was really from the British city of Manchester when they met at a Commonwealth meeting this week.
Sethi -- whose mother was born in Guyana -- said Charles asked her where she was from and when she replied, said: "Well, you don't look like it!" and laughed.
She wrote in The Guardian that she felt humiliated and angry, adding that "some people, including the prince, urgently need a history lesson about immigration".