Thousands packed the royal park close to Buckingham Palace, and thousands more munched on "Diamond Jubilee Chicken" and other festive foods at a picnic in the palace garden on the third day of events to mark Elizabeth's long reign.
"I'm very excited. It's just brilliant that's she's been with us for so long .... It makes you feel great to be British. Everybody likes her," said teacher Sally Conway, 47, wearing a Union Jack hat, while her mother wore a flag-themed feather boa.
The concert, starting at 1830 GMT, takes place 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The festivities have demonstrated the renewed popularity of a royal family once mired in scandal and dismissed as outdated, and the celebrations over an extended holiday weekend are a boon for Britons battered by recession and harsh state spending cuts.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 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.
Paul McCartney and Stevie Wonder teased the crowds with sound checks for the evening's concert, where they will entertain the 86-year-old monarch and 10,000 other ticket holders at a circular stage in front of Buckingham Palace.
Tom Jones said he was keeping his set list a surprise, 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.
The jubilee ends on Tuesday with a thanksgiving service at St Paul's Cathedral, a carriage procession along the Mall avenue, a Royal Air Force flypast and a farewell wave from the royal family to crowds gathered in front of Buckingham Palace.
BEACONS
Take That frontman Gary Barlow was brought in to organise the concert, and has penned a song for the jubilee with musical impresario Andrew Lloyd Webber. Barlow said he had received requests from the royal household for particular artists.
"What we've tried to do musically is pick that span right across her reign, someone from every decade of the 60 years, and so we're really hopeful for a really momentous and celebratory occasion," Barlow told the BBC.
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, a network of 4,000 beacons will be lit 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.
His group estimates that the royal family, which officially sets taxpayers back between 30 million and 40 million pounds a year, in fact costs closer to 200 million pounds when security and travel are included.
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.
Copyright 2015 Thomson Reuters. All rights reserved.
