96-round gun salute for Queen Elizabeth II as state mourning begins

An official period of state mourning is underway in the United Kingdom on Friday, a day after Queen Elizabeth II died, and there has been an outpouring of grief from members of the public who have been laying flowers at royal residences around the country for its longest-reigning monarch.

In London, 96 rounds of gun salutes -- one for every year of the Queen's life -- have been fired in tribute to the late monarch from the Tower of London and Hyde Park by the King's Troop Royal Horse Artillery and the Honourable Artillery Company.

Churches also tolled their bells, after the Church of England sent out guidance to parishes, chapels and cathedrals across the country encouraging them to open for prayer or special services. Major sporting events, including football and cricket matches, have been postponed as a mark of respect.

British Prime Minister Liz Truss led tributes at a special joint Parliament session convened to pay tribute to the Queen, who died at her Balmoral Castle residence in Scotland on Thursday.

The regular business of government is at a halt, unless anything urgent occurs, with the focus to fall entirely on the Queen during the 10-hour sitting of Parliament.

Truss said that since the death of the Queen was announced there has been the "most heartfelt outpouring of grief" across the world.

"Everyone who met her will remember the moment. They will speak of it for the rest of their lives. Even those who never met her, her late majesty's image is an icon for what Britain stands for as a nation," she said, reiterated her earlier statement describing the late monarch as the “rock on which modern Britain was built”.

With reference to the Queen's heir King Charles III, she told the Commons that the nation will offer its "loyal service to our new King".

Truss and senior ministers attended the public service of remembrance at St. Paul's Cathedral in central London and then the government is due to confirm the length of national mourning, which is likely to be around 12 days, from now up to the day after the Queen's funeral.

The funeral day will be a public holiday in the form of a Day of National Mourning.

Overnight on Thursday, crowds gathered outside Buckingham Palace in London and also at Windsor Castle in Berkshire, with many in tears as they paid their personal tributes to Britain's longest-serving monarch who died aged 96 after a 70-year reign.

"In 1953 Her Majesty defined our family of nations as one which 'bears no resemblance to the empires of the past'... Her Majesty's vision for the Commonwealth at the beginning of her reign has been fulfilled, fuelled by her dedication and commitment," said Baroness Patricia Scotland, Secretary-General of the Commonwealth.

WATCH: 96-round gun salutes fire for the Queen

The Mall, near the Commonwealth Secretariat leading up to Buckingham Palace, was lined up one by one with the iconic London black cabs turning out to pay tribute to the Queen with their headlights on. All of the UK capital's bus stops also had imagery honouring the Queen and the famous Piccadilly Circus screen flashed images of the Queen.

The hereditary monarchy has passed to her son and heir, King Charles III, who with his wife -- Queen Consort Camilla -- returned to London from Balmoral with the late monarch.

"We mourn profoundly the passing of a cherished Sovereign and a much-loved mother. I know her loss will be deeply felt throughout the country, the Realms and the Commonwealth, and by countless people around the world," said King Charles in a statement.

"During this period of mourning and change, my family and I will be comforted and sustained by our knowledge of the respect and deep affection in which the Queen was so widely held," he said.

King Charles will meet the Earl Marshal, the Duke of Norfolk, who is in charge of the Queen's funeral, to sign off on the pre-set schedule for the coming days under Operation London Bridge. The 73-year-old King will decide on the length of court or royal mourning for members of the royal family and royal households.

"Following the death of Her Majesty The Queen, it is His Majesty The King's wish that a period of royal mourning be observed from now until seven days after The Queen's funeral," Buckingham Palace said in a statement.

The date of the funeral will be confirmed in due course, the palace said.

Royal mourning will be observed by members of the royal family, royal household staff and representatives of the royal household on official duties, together with troops committed to ceremonial duties.

Royal residences, including the Royal Mews at Buckingham Palace, will close until after the Queen's funeral. According to the palace, there will be no physical books of condolence at the royal residences and instead an online book has been opened on the royal website.

Charles' first televised address to the nation as King on Friday evening will pay tribute to his mother as he pledges to serve the country as Head of State.

On Saturday, there will be a special session of the House of Commons for members of Parliament to take an oath of allegiance to King Charles III and end in a “formal humble address to His Majesty The King”.

Alongside, an Accession Council will meet at. St James's Palace in London to formally proclaim Charles as the new sovereign. The first public proclamation of the new sovereign will then be read in the open air from the Friary Court balcony at St. James's Palace by the Garter King of Arms.

Union flags, which are flying at half-mast across the country, go back up to full-mast at 1 pm and remain there for 24 hours to coincide with the proclamations before returning to half-mast in mourning.