London, United Kingdom | Tickets to Britain's Queen Elizabeth II's 90th birthday celebrations sold out within hours  as Buckingham Palace promised four days of pageantry "fit for the queen" including dancing and horse shows.

Britain's longest-ever reigning monarch, Elizabeth turns 90 on April 21 next year and the palace has organised a public celebration lasting four days at Windsor Castle, one of her residences outside London.

The 25,000 tickets for the events between May 12-15 cost up to £165 (234 euros, $249), with the most expensive places situated next to the "Royal Enclosure" where royals might attend.

The queen herself will attend the finale on Sunday and proceeds from the sale will go to charity, Buckingham Palace said.

Those unable to buy tickets can still apply for one of 5,000 free slots, allowing them to watch the ceremony on a screen and watch celebrities arrive.

The ceremonies will involve 900 horses and 1,500 artists including dancers, musicians and actors from around the world, the palace said.

Around 100 bagpipe players will also take part.

The queen is expected to celebrate her actual birthday in private and then take part in an official yearly ceremony known as the Trooping the Colour in June.