Britain marked Queen Elizabeth's 91st birthday on Friday with gun salutes, as the monarch herself enjoyed a family day and a trip to the races.

The queen, who owns and breeds racehorses, was spotted smiling broadly and chatting animatedly Friday with jockeys and staff at Newbury Racecourse, not far from her Windsor Castle home.

She visited the racecourse with daughter Princess Anne and sat in the royal box to watch her thoroughbred Maths Prize run; it finished fifth.

There were also official celebrations in London, where a troop of the Royal Horse Artillery rode horse-and-gun carriages past Buckingham Palace before staging a 41-gun salute in Hyde Park at noon.

Members of the King's Troop Royal Horse Artillery take part in a ceremonial 41- gun salute in Hyde Park on Friday to mark the Queen's birthday. (Alastair Grant/Associated Press)

Outside the palace, a band of guardsmen in scarlet tunics and bearskin hats played Happy Birthday during the Changing of the Guard ceremony.

And at the centuries-old Tower of London, there was a second salute with 62 guns.

The queen is Britain's oldest and longest-reigning monarch, having become queen on Feb. 6, 1952. She is also the world's longest-reigning living monarch since the death of Thailand's King Bhumibol Adulyadej last year.

The celebratory gun salute in Hyde Park on Friday included firing 13-pounder field guns. (Alastair Grant/Associated Press)

Elizabeth also has an official birthday, marked in June — when the British weather is better — with the Trooping the Colour" military parade.