LONDON (Reuters) - 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 hospitalized.
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 honor 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 traveled 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 ex-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.
The festivities have demonstrated the renewed popularity of a royal family once mired in scandal and dismissed as outdated, and the celebrations over an extended holiday weekend are a boon for Britons battered by recession and harsh state spending cuts.
Coverage in Britain's often fractious newspapers was gushing: "After 60 years on the throne the Queen is, more than ever, an embodiment of our pride and a focus of our patriotism," The Times said its souvenir jubilee edition.
Music stars performing at the evening concert lined up to sing the 86-year-old queen's praises.
"The monarchy has taken quite a lot of hits in its time. And we turned a corner, it seems to me, when William and Catherine got married," singer Cliff Richard told Sky News, referring to last year's wedding of Elizabeth's grandson Prince William to Kate Middleton, an event that boosted the royal family's image.
Welsh crooner Tom Jones said his set would include "Mama Told Me Not to Come", while Shirley Bassey will sing "Diamonds Are Forever" and Ska band Madness will sing 1980s hit "Our House" from the palace roof.
The BBC promised "one of the most spectacular shows ever staged in the UK". Television viewer figures are expected to be large, after Sunday's flotilla attracted an average audience of 10.3 million, or 60 percent of viewers, the BBC said.
Take That frontman Gary Barlow was brought in to organize the concert, and has penned a song for the jubilee with musical impresario Andrew Lloyd Webber.
The souvenir album "Sing", featuring acts from across the Commonwealth of mostly former British colonies, went straight to number one in the album charts on Sunday.
After the concert, the last in a network of more than 4,000 beacons will be lit to accompany others across Britain and the Commonwealth, leading into Tuesday, the final day of the extended holiday weekend.
By 1500 GMT, beacons had already been lit in Tonga, New Zealand and Australia.
Millions of Britons have spilled onto streets bedecked in Union Jack bunting up and down the country for outdoor parties during the jubilee holiday.
Support is not universal however. Views range from indifference - about two million Britons travelled abroad to benefit from the extra days off - to outright opposition.
"Her achievement is just staying alive, doing little and saying less," Graham Smith, head of campaign group Republic, told Reuters.
Elizabeth is only the second monarch to mark 60 years on the throne - her great-great-grandmother Queen Victoria reached the milestone in 1897. She is also on course to become the longest-serving British sovereign in 2015.
The queen's reign began in 1952, when she was 25, and has spanned 12 prime ministers from Winston Churchill to David Cameron.
Additonal reporting by Paul Hackett; editing by Rosalind Russell