London (AFP) -
Britain went into full celebration mode Saturday to honour Queen Elizabeth II's 70 years on the throne, as a 'party at the palace' concert got under way featuring an array of stars including Diana Ross and Andrea Bocelli.
The concert, the climax of the third day of public events to mark the 96-year-old monarch's record-breaking Platinum Jubilee, saw 22,000 ticket-holders pack a purpose-built 360-degree stage outside the queen's central London residence.
Tens of thousands more thronged the city centre while millions watched on television as rockers Queen + Adam Lambert opened the star-studded show with renditions of 'We Will Rock You', 'Don't Stop Me Now' and 'We Are The Champions'.
'We're exceedingly honoured and exceedingly happy to be here, it means a lot to us,' guitarist Brian May said beforehand.
May provided one of the most enduring images from the 2002 jubilee, playing 'God Save the Queen' on the roof of Buckingham Palace.
As Saturday's concert got started, the monarch made a surprise on-screen appearance, starring in a comedic pre-recorded scene taking tea with Britain's beloved children's book and film character Paddington Bear.
'Happy Jubilee, ma'am, and thank you. For everything,' the bear told her.
'That's very kind,' the queen replied, before the pair began to tap out the drum beat to 'We Will Rock You' on their tea saucers with silver spoons.
- 'Momentous' -
Motown legend Ross -- performing for the first time in Britain in 15 years -- Italian opera star Bocelli and James Bond composer Hans Zimmer were also to perform later in the evening.
Ross, who heads to the Glastonbury Festival this month after Saturday's concert, said she was 'absolutely delighted to receive an invitation to perform on such a momentous occasion'.
Heir-to-the-throne Charles has previously revealed that the 78-year-old diva's disco hit 'Upside Down' from 1980 was one of his favourite tracks.
Others set to take the stage include Alicia Keys, Rod Stewart, George Ezra and Eurovision 2022 runner-up Sam Ryder. Elton John has recorded a tribute.
The queen -- the longest-reigning monarch in British history -- was not attending the two-and-a-half-hour event in person but was watching on television in Windsor Castle.
On Thursday, the first day of celebrations, she made two public appearances to huge crowds on the Buckingham Palace balcony, and then travelled to Windsor to attend a beacon-lighting ceremony.
The effort, after months battling difficulties walking and standing, left her in 'some discomfort', Buckingham Palace said.
She withdrew from a Friday church service of thanksgiving and missed the flat-racing showcase The Derby Saturday for only the fourth time since 1952.
- 'Binds us' -
Charles, 73, and his eldest son, Prince William, 39, joined other dignitaries in a royal viewing box at the concert and were expected to address the crowds.
But Prince Harry and wife Meghan, who sensationally quit British royal life for California in January 2020 but are visiting for the jubilee, were notably absent.
It was their second child Lilibet's birthday Saturday, with the queen wishing her namesake great-granddaughter a 'very happy first birthday' on Twitter after reportedly meeting her for the first time in recent days.
Jubilee celebrations began Thursday with the pomp and pageantry of the Trooping the Colour military parade to mark the sovereign's official birthday.
Friday's focus was the traditional Church of England service led by senior royals -- and returning Prince Harry and his wife Meghan -- in the hallowed surroundings of St Paul's Cathedral.
Britain made Thursday and Friday public holidays to mark the unprecedented milestone in the queen's reign, which has focused attention on the monarchy's future without her.
Longer pub opening hours, street parties and other celebratory events have temporarily lifted the gloom of a soaring cost-of-living crisis.
'I'm proud of Britain and it's nice to be able to celebrate as well,' said London bus driver June Davis, in Windsor Saturday to enjoy the atmosphere.
'The queen is a constant thread through all our lives, she binds us all together.'
Sunday will see millions of people share food at 'Big Jubilee Lunch' picnics and take part in a musical and creative public pageant with a cast of 10,000.
Ed Sheeran will round off the celebrations Sunday, singing his 2017 hit 'Perfect'.