Britain is marking Queen Elizabeth II's 91st birthday with gun salutes, as the monarch celebrates quietly at home.

A troop of the Royal Horse Artillery will ride horse-and-gun carriages past Buckingham Palace before staging a 41-gun salute in Hyde Park at noon (1100GMT). There will also be a 62-gun salute at the Tower of London an hour later.

The queen is Britain's oldest and longest-reigning monarch, having become queen on Feb. 8, 1952. She is also the world's longest-reigning living monarch since the death of Thailand's King Bhumibol Adulyadej last year.

The queen usually spends her birthday privately. She also has an official birthday, marked in June - when the weather is better - with the "Trooping the Color" military parade.