Britain's Queen Elizabeth II celebrates her 90th birthday today. This portrait with her only daughter, Princess Anne, is one of three official portraits released by Buckingham Palace to mark the occasion.

LONDON — Queen Elizabeth II, Britain’s oldest and longest-serving monarch, is celebrating her 90th birthday today with a day at home and a short walk.

Her government and subjects are adding gun salutes, fireworks, tributes in Parliament and televised retrospectives of a life that has stretched from the Roaring ’20s to the Internet age.

The queen was born Princess Elizabeth on April 21, 1926, and became queen on the death of her father, King George VI, in 1952, when she was only 26.

In a birthday message, Prime Minister David Cameron said the queen “has lived through some extraordinary times,” from World War II to the moon landing, the end of the Cold War and advent of peace in Northern Ireland. He said “Her Majesty has been steadfast — a rock of strength for our nation, for our Commonwealth and on many occasions for the whole world.”

Cameron will lead tributes later in Parliament, which will be lit up overnight in the red, white and blue of the Union Jack flag.

The queen is spending the day at Windsor Castle and will greet well-wishers on a walk through west of London.

Elsewhere, the day was being marked with an eruption of pomp. Artillery companies will fire gun salutes from Hyde Park and the Tower of London, while the bells of Westminster Abbey will ring.

Buckingham Palace issued three portraits to mark the day. One shows the queen surrounded by seven young grandchildren and great-grandchildren. Another shows the queen with Princess Anne, her only daughter. The third shows her with four of her beloved dogs.