Singer Robbie Williams performs during the diamond jubilee concert at Buckingham Palace in London.

London - Robbie Williams kicked off a concert outside Queen Elizabeth's sumptuous London residence on Monday before huge crowds gathered to celebrate the monarch's 60 years on the throne, but the event was overshadowed by news her husband had been admitted to hospital.

Prince Philip, who turns 91 next weekend, was taken to hospital with a bladder infection in what Buckingham Palace said was a “precautionary” move.

He will remain under observation for a few days, meaning he will miss the latter stages of the queen's Diamond Jubilee celebrations, but the monarch was expected to attend Monday's gig featuring pop royalty like Paul McCartney and Stevie Wonder.

On Tuesday the queen will be without her husband of 64 years when she attends a thanksgiving service at St Paul's Cathedral, leads a carriage procession through London and waves to supporters beneath the balcony of Buckingham Palace.

Hundreds of thousands of cheering, flag-waving people from around the world packed the grand red road leading to the 775-room palace to honour the queen and watch a pop concert on the third of four days of nationwide festivities.

“Being Germans, we would like to be a bit more British!” said Josef Fischer, 60, who travelled with his wife and three children from Bavaria to join the jubilee celebrations.

“On these days you forget everything else. You have fun, you feel good and the troubles come when you go back home.”

Williams opened the show with Let Me Entertain You, and former Beatle McCartney was due to close.

“When you think about what it is - 60 years of Her Majesty's reign, and we're all here having a party and people from all over Britain, all over the world are celebrating this woman,” McCartney told the BBC.

“She's only one woman after all. You look at the ordinary policeman - he does 20 years then retires. She's done 60 years and she's still going strong so she's amazing. I think she's a really good example for Britain and she's a great family woman.”

The concert came a day after more than a million people braved heavy rain to watch a 1 000-strong flotilla make its way down the River Thames through the heart of London, led by the queen aboard a gilded royal barge festooned with flowers. - Reuters