With a little luck, Monday night's star-studded musical tribute to Queen Elizabeth II will go more smoothly than the rehearsal, with more fireworks and less fire.

A blaze that broke out in a roof apartment forced the evacuation of Buckingham Palace on Sunday evening, interrupting preparations for the outdoor concert and marring the high-spirited four-day celebration of Elizabeth's 50 years on the throne.

Palace spokeswoman Ailsa Anderson told The Associated Press on Monday that the London Fire Brigade was still investigating the cause of the blaze. Palace spokesman Simon Walker told the British Broadcasting Corp. that the fire did not occur in an area being used for the Jubilee.

``What we do know is it is nothing to do with the concerts or any of the arrangements to do with the Jubilee,'' Walker said. ``It is in a part of the palace that is not being used.''

No royal family members were in the palace when the fire started, fire officials said.

When the alarm sounded shortly after 6:30 p.m., Ozzy Osbourne had just finished rehearsing outside. BBC reported that those evacuated from the area around the palace included musicians Phil Collins, Eric Clapton and Queen guitarist Brian May.

The concert was expected to be a high point of the national Golden Jubilee celebrations, and the palace promised it would go ahead as scheduled.

Also among those scheduled to perform for 12,000 guests and a live television audience are Paul McCartney, Annie Lennox and former Beach Boy Brian Wilson.

``There is an enormous crowd of extremely famous people here sitting on the lawn chatting on their mobile phones,'' May told the BBC while the fire was burning.

The blaze was brought under control within an hour and a half, said Colin Williamson, a Fire Brigade spokesman. Outdoor rehearsals resumed and workers re-entered palace later Sunday evening.

When the fire was at its height, smoke poured from one area of the roof as firefighters with masks, air tanks and hoses worked nearby. Twenty fire engines rushed to the palace, Williamson said.

Rescuers escorted four palace staff who had been working on the roof to safety, firefighter Steve Newman said. One firefighter was hit by a piece of equipment and suffered cuts and bruises around his eye, Newman said, but there were no other injuries.

The palace said in a statement that a fire alarm system had detected the flames in an apartment above the East Gallery, a large corridor that connects the palace ballroom to the state rooms.

Spokeswoman Penny Russell-Smith told the BBC it was unclear how the fire started, but police said it was not set intentionally.

The state rooms are at the heart of the palace and are used regularly by the queen and other royals for entertaining. The ballroom, which first opened in 1856, is often used by the queen for ceremonies awarding titles and royal honors.

The damage caused by the fire did not appear to be anywhere near as bad as that done by blazes at Windsor Castle in 1992 and at Hampton Court Palace in 1986. Buckingham Palace said two areas of ceiling had been damaged and water from burst pipes soaked some carpets.

Firefighter Brian Robinson said there was also some minor smoke damage, but that no royal treasures or artifacts had been harmed.

Sir Hugh Roberts, director of the royal collection, was inspecting artworks and other valuable items for signs of damage, and the palace said two paintings were removed as a precaution.

Roberts told Prince Charles about the fire, and a spokeswoman said the heir to the throne was shocked by the blaze but relieved that no one was seriously hurt.

Eighteen royals and 12,000 guests attended a spirited classical music concert on the palace grounds Saturday night and excitement was building for Monday's show.

May, the Queen guitarist, was to open the concert by playing ``God Save the Queen'' from the palace roof and supporters around the world are expected to light a chain of 2,000 beacons, culminating in a fireworks display launched from atop the palace.

It was not clear whether the fire would force organizers to modify any of those plans.

The queen and her husband Prince Philip planned to attend a parade in Windsor on Monday, and hundreds of street parties were to be held across the country.

The celebrations are also scheduled to include an elaborate royal procession to a service at St. Paul's Cathedral on Tuesday.

The 1986 fire wrecked a wing of Hampton Court Palace and killed one resident. The 1992 Windsor Castle fire gutted 100 rooms, caused tens of millions of dollars in damage and contributed to the difficulties of the year Elizabeth dubbed her ``annus horribilis.''

Elizabeth, 76, was 25 when she became queen upon the death of her father, George VI, in 1952.