Britain's royal family and Prime Minister Boris Johnson attended a service of thanksgiving for Queen Elizabeth on Friday, the second day of her Platinum Jubilee celebrations, although the monarch herself was missing due to ongoing mobility issues.

Four days of events kicked off on Thursday, when a beaming Elizabeth waved to crowds from the balcony of Buckingham Palace after a military parade and Royal Air Force flypast, and later led the lighting of the Principal Platinum Jubilee Beacon at her Windsor Castle home.

The celebrations continued with a National Service of Thanksgiving at London's St Paul's Cathedral to pay tribute to the sovereign's 70 years on the throne.

But the queen, who is 96 and has been forced to cancel a series of engagements recently due to "episodic mobility problems", reluctantly pulled out of Friday's service.

Buckingham Palace said she had experienced "some discomfort" during Thursday's events, and the journey to London from Windsor Castle, where she spends most of her time these days, and the activity involved for the service was too much.

Her son and heir Prince Charles, 73, instead represented the monarch, who is a devout Christian and also the titular head of the Church of England. She, instead watched the service on television at her home in Windsor Castle near London.

All eyes were on the queen's grandson Prince Harry and his wife Meghan, as they arrived, making their first public appearance together in Britain since stepping down from royal duties two years ago.

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