Queen Elizabeth II, Britain's longest-reigning monarch has died aged 96, Buckingham Palace said on Thursday.
Christian leaders across the world have called for prayers.
Most Rev Justin Welby, Archbishop of Canterbury said “It is with profound sadness that I join the nation, the Commonwealth and the world in mourning the death of Her Late Majesty The Queen. My prayers are with The King and the Royal Family. May God draw near them and comfort them in the days, weeks and months ahead.
“As we grieve together, we know that, in losing our beloved Queen, we have lost the person whose steadfast loyalty, service and humility has helped us make sense of who we are through decades of extraordinary change in our world, nation and society”.
Most Rev Stephen Cottrell, Archbishop of York said: “In Her Majesty’s first Christmas broadcast, ahead of her Coronation she asked the nation, whatever their religion, to pray that God would give her wisdom and strength to carry out the solemn promise she would be making and to faithfully serve God and us all the days of her life.
“That is most definitely a prayer that has been answered. Her service to our nation and Commonwealth has been exemplified by her devotion to her duty, which has always been offered with joy. Underpinning this has been her deep faith in God and in her we have witnessed God’s faithfulness at work”.
The Queen’s eldest son Charles, the former Prince of Wales, now becomes King.
King Charles released a statement saying: "The death of my beloved mother HM the Queen is a moment of the greatest sadness for me and all members of my family."
Members of the Queen's family spent Thursday afternoon travelling to Aberdeenshire to be there.
Pope Francis said he was deeply saddened by the death of the Queen and offered his condolences to her family and her successor, King Charles.
"I willingly join all who mourn her loss in praying for the late Queen’s eternal rest, and in paying tribute to her life of unstinting service to the good of the Nation and the Commonwealth", Francis said in a telegram to King Charles."
Cardinal Vincent Nichols, Archbishop of Westminster and President of the Catholic Bishops' Conference of England and Wales said: "On 21 April 1947, on her twenty-first birthday, Princess Elizabeth said, ‘I declare before you all that my whole life whether it be long or short shall be devoted to your service.’
"Now, seventy-five years later, we are heartbroken in our loss at her death, and so full of admiration for the unfailing way in which she fulfilled that declaration.
"Even in my sorrow, shared with so many around the world, I am filled with an immense sense of gratitude for the gift to the world that has been the life of Queen Elizabeth II.
"At this time, we pray for the repose of the soul of Her Majesty. We do so with confidence, because the Christian faith marked every day of her life and activity".
Most Rev Michael Bruce Curry, Presiding Bishop and Primate of The Episcopal Church has also paid tribute.
He said in a statement: “Today we mourn the passing and celebrate the life and legacy of Queen Elizabeth II. My prayers for peace go out for her, for her loved ones, and for all those who knew and loved her throughout the world.
“Her resilience, her dignity, and her model of quiet faith and piety have been—and will continue to be—an example for so many. May she rest in peace and rise in glory.”
His Eminence Archbishop Angaelos, first Coptic Orthodox Archbishop of London honoured the Queen for her "faithful witness and commitment to her Christian faith"
"She is quite simply unmatched in her legacy, having served faithfully and joyfully as Monarch for over seventy years, longer than any other monarch in British history; a testament to her character and strength of resolve," he said. She is also the only monarch that most of us will have ever known.
"Over the course of her reign, Her Majesty used her position for good, serving the nation through tireless visits to various charities and organisations that serve the wider community and the most vulnerable. She is known widely for always taking her duty as monarch and a daughter of Christ seriously, evident in the way she spoke and interacted with people from all backgrounds, and in the messages shared with the world every Christmas and Easter among other special moments throughout the year. Her Majesty’s uplifting and optimistic spirit was especially heartening at times of challenge over the course of her reign".