The funeral service to remember Britain's longest-reigning monarch, Queen Elizabeth II, is taking place at Westminster Abbey, reports BBC.
Among the guests are world leaders including US President Biden and hundreds of other foreign dignitaries.
The Dean of Westminster, who is leading the service, expressed gratitude for the Queen's "life-long sense of duty".
King Charles III led a sombre procession behind his mother's coffin from Westminster Hall to the abbey.
The Dean, the Very Rev David Hoyle, began the service by speaking of the Queen's "unswerving commitment to a high calling over so many years as Queen and Head of the Commonwealth".
"With admiration we recall her life-long sense of duty and dedication to her people," he said.
The service has been filled with traditional church music and readings from the Bible.
As the Queen's coffin entered Westminster Abbey the choir sang lines, known as the Sentences, put to music which has been used at every state funeral since the early 18th century.
Prime Minister Liz Truss read to the mourners from John 14 and the congregation sang The Lord's My Shepherd - a hymn sung at the wedding of the Queen to the Duke of Edinburgh.
The Archbishop of Canterbury, the Most Reverend Justin Welby, gave the sermon and quoted the singer Dame Vera Lynn - saying "we will meet again".
The phrase was used by the Queen in a rare address to the nation at the beginning of the Covid pandemic.
The archbishop said: "The grief of this day - felt not only by the late Queen's family but all round the nation, Commonwealth and world - arises from her abundant life and loving service, now gone from us."
Towards the end of the service, the Last Post will be played before a two-minute national silence.
The Queen's coffin was conveyed - in the first of three processions throughout the day - from Westminster Hall where she was lying in state since Wednesday.
The Prince of Wales and the Duke of Sussex walked side-by-side behind their father, the King. The King walked alongside his siblings, the Queen's four children.
The procession to the abbey saw the State Gun Carriage carry the coffin, drawn by 142 sailors, while the sound of pipes and drum rang out.
US President Joe Biden, French President Emmanuel Macron and Canadian Prime Minister Justin Trudeau are among the world leaders at the funeral.
Some 2,000 mourners are bidding farewell to the Queen at the state funeral, including 500 dignitaries - with presidents, prime ministers and foreign royalty among the guests.
There are also members of many European royal families, including Belgium, the Netherlands, Spain and Denmark, as well as the Emperor and Empress of Japan.
Former prime ministers Theresa May, Tony Blair, David Cameron, Gordon Brown, John Major and Boris Johnson are also at the historic abbey.
About 200 people who were recognised in the Queen's birthday honours also received invitations.
Knife crime campaigner Natalie Queiroz told BBC Breakfast she was "totally speechless" when she was asked to attend.
Barbara Crellin, a volunteer emergency responder, said she "just cried and cried" when she was invited and described herself as "so humbled and privileged to be here".
The event is expected to be watched by millions of people across the country, and most workplaces are closed for a bank holiday.
It is also expected to be watched by millions around the world, with the Queen the head of state for 14 realms throughout the Commonwealth.
For those not invited big screens have been put up in cities across the country, while some cinemas, pubs and other venues are also showing the once-in-a-generation event.
This is the first state funeral to be held since Sir Winston Churchill's in 1965.
Following the service, the coffin will be drawn in a walking procession from the Abbey to Wellington Arch, at London's Hyde Park Corner, to the sombre toll of Big Ben.
Gun salutes will also fire every minute from Hyde Park during the procession and people can watch in person from designated viewing areas along the route.
Once at Wellington Arch, at about 13:00, the coffin will be transferred to the new State Hearse for its final journey to Windsor Castle. There, the Queen's coffin will enter St George's Chapel for a committal service.
Attended by a smaller congregation of about 800 guests, the committal service will be conducted by Dean of Windsor David Conner, with a blessing from the Archbishop of Canterbury.
At a private family service later, the Queen will be buried alongside her late husband, the Duke of Edinburgh, at the King George VI memorial chapel, located inside St George's Chapel.