London: Gun salutes took place across Britain on Thursday to celebrate the 90th birthday of the country's longest reigning monarch -- Queen Elizabeth II. Well-wishers from across the world gathered outside the Windsor Castle and the town of Windsor to celebrate the Queen's birthday, Xinhua news agency reported. Some people even camped out overnight so that they could get a better spot to see the Queen. Prince Charles paid his tribute to his mother through a special radio broadcast on Thursday morning, in which he read an edited passage from William Shakespeare's King Henry VIII. British Prime Minister David Cameron said: "Her Majesty has devoted her entire life to the service of others representing our country, and carrying out all her duties with extraordinary grace and humility. Rarely has anyone in public life served for so long, served so brilliantly, worked so hard, and brought so many people together." "And in this modern Elizabethan era, in which so much around her has changed, Her Majesty has been steadfast, a rock of strength for our nation, for our Commonwealth, and on so many occasions, for the whole world. She is our Queen and we could not be more proud of her," Cameron said. Accompanied by Prince Philip, the Queen arrived at Windsor Castle at noon, met people there and then walked through the streets of Windsor. The crowds were singing Happy Birthday to her. The Queen came to throne in February 1952 and was coronated on June 2, 1953. She celebrates two birthdays each year, one is the day she was born on April 21, and another is an official birthday in June. A range of splendid celebrations will be held in the grounds of Windsor Castle from May 12-15, as well as from June 10-12.