By Edouard Guihaire
Britain has celebrated Queen Elizabeth II becoming the country's longest-reigning monarch, a milestone the 89-year-old herself downplayed.
The bells of Westminster Abbey rang out in London on Wednesday (local time) as Prime Minister David Cameron paid tribute in parliament to her 63-year reign as a "golden thread running through three post-war generations".
"Inevitably, a long life can pass by many milestones. My own is no exception," the queen told a cheering crowd of supporters waving British and Scottish flags as she opened a railway line in Scotland.
She said the landmark was "not one to which I have ever aspired".
"But I thank you all and the many others at home and overseas for your touching messages," said the queen, who wore a diamond-studded brooch that once belonged to the previous record holder - her great-great-grandmother Queen Victoria.
"Today Queen Elizabeth II has officially become the longest reigning British Monarch," read a tweet published on the dot on the monarchy's Twitter page.
She has served more than 23,226 days on the throne - a reign spanning from the gloom of the post-war years to the digital age, with a few royal scandals causing blushes along the way.
She is to host a private dinner later on Wednesday (local time) at Balmoral Castle - her traditional summer residence in Scotland - with her grandson Prince William and his wife Kate in attendance.
"She is our queen and we could not be more proud of her," Cameron told parliament.
"She has served this country with unerring grace, dignity and decency and long may she continue to do so."
Elizabeth became queen upon the death of her father George VI, Britain's king during World War II, whose stammer inspired the Oscar-winning film The King's Speech.
Royal sources said she was not keen to celebrate because of the painful memory of his death.
Her reign has lasted through 12 British prime ministers, starting with wartime leader Winston Churchill, who was a mentor to the young queen.
She has steered the monarchy through some rocky patches, including public anger at her reaction to Princess Diana's death in 1997, which some saw as cold.
Outside Buckingham Palace on Wednesday (local time), wellwishers from around the world gathered to celebrate.
"It's a very special day, we are very privileged to be here, to share this moment with everyone else in the world," said Janice Gallagher, 68, from Australia.