Etching a special place in history, Queen Elizabeth II today became Britain's longest-reigning monarch after surpassing Queen Victoria's rule of over 63 years, as heart-felt tributes, fanfare and a gun salute marked the momentous occasion.


Dressed in turquoise with her trusty black handbag at her side, the Queen smiled and waved to those gathered at the Waverley Station on the day she passes the record set by her great-great-grandmother Queen Victoria to board the new Borders Railway.


The 89-year-old, who is also the nation's oldest ever monarch, has met most of the major figures of recent decades, from India's first Prime Minister Jawaharlal Nehru to Japanese emperor Hirohito.


She will officially become the longest-serving monarch in British history at 1730 (local time) when her reign would have completed 63 years and seven months -- calculated at 23,226 days, 16 hours and approximately 30 minutes.


British Prime Minister David Cameron led the tributes to the Queen Elizabeth as he described the 89-year-old ruler as a "rock of stability" and her service to the nation as "truly humbling" in an era when so much had changed.


"The reign of Queen Elizabeth has been a golden thread running through three post-war generations, and she's presided over more than two-thirds of our history as a full democracy with everyone being able to vote," he said in the House of Commons, where usual business was postponed for the special tributes.


"Her selfless sense of service and duty have earned her unparalleled respect and admiration not only in Britain but around the world. The Queen is our Queen and we could not be more proud of her. She has served this country with an unerring grace, dignity and decency and long may she continue to do so," Cameron said.


The Queen and Prince Philip travelled by train to Tweedbank, in the Borders region, with Scotland's First Minister Nicola Sturgeon. They stopped off in Newtongrange where the Queen accepted flowers from well-wishers and opened the new railway station.


The Queen paid a personal tribute to her great-great grandmother by wearing a diamond brooch owned by Queen Victoria and passed down to her by Queen Mary. The brooch is one of a set of three ordered by Queen Victoria from the royal jeweller Garrard, made with 506 diamonds she supplied.


The Queen took time out from her traditional summer break at this time of year at her private Scottish home, Balmoral Castle, to open the new railway but overall had wanted today to be business as usual. HMS Belfast docked on river Thames sounded a four gun salute to mark the occasion.