LONDON — Britain’s new king prepared to meet with the prime minister Friday and address a nation mourning Queen Elizabeth II, the only British monarch most of the world had known and a force of stability in a volatile age.

The country began a 10-day mourning period Friday, with bells tolling around Britain and 96-gun salutes planned in London — one for each year of the queen’s long life. People around the globe gathered at British embassies to pay homage to the queen, who died Thursday in Balmoral Castle in Scotland.

King Charles III, who spent much of his 73 years preparing for the role, takes the throne in an era of uncertainty for both his country and the monarchy itself. In Britain and across its former colonies, the widespread admiration for Elizabeth herself was sometimes mixed with criticism of the institution and the imperial history she represented.

On the king’s first full day of duties Friday, he and his wife Camilla, the Queen Consort, left Balmoral to head to London. He is expected to meet Prime Minister Elizabeth “Liz” Truss, appointed just days earlier, and deliver a speech to the nation at a time when many Britons are preoccupied with an energy crisis, the soaring cost of living, the war in Ukraine and the fallout from Brexit.

Hundreds of people arrived through the night to leave flowers outside the gates of Buckingham Palace, the monarch’s London home, or simply to pause and reflect.

Finance worker Giles Cudmore said the queen had “just been a constant through everything, everything good and bad.”

“She’s just been the foundation of my life, the country,” he said.

Everyday politics was put on hold, with lawmakers set to pay tribute to the monarch in Parliament over two days, starting at noon. Many sporting and cultural events were canceled as a mark of respect, and some businesses — including Selfridges department store and the Legoland amusement park — shut their doors.

Archbishop of Canterbury Justin Welby said the queen’s death marked an “enormous shift” for Britain and the world.

“A part of our lives we’ve taken for granted as being permanent is no longer there,” he said.

Elizabeth was Britain’s longest-reigning monarch and a symbol of constancy in a turbulent era that saw the decline of the British empire and disarray in her own family. Members of the royal family had rushed to her side at the family’s summer residence in Balmoral after her health took a turn for the worse.

On Friday, Ms. Truss and other senior ministers are expected to attend a remembrance service at St. Paul’s Cathedral in London. Charles, who became the monarch immediately upon his mother’s death, will then be formally proclaimed king at a special ceremony Saturday.

After a vigil in Edinburgh, the queen’s coffin will be brought to London, and she will lie in state for several days before her funeral in Westminster Abbey.

As the second Elizabethan Age came to a close Thursday, the BBC played the national anthem, “God Save the Queen,” over a portrait of the monarch in full regalia as her death was announced. The flag over Buckingham Palace was lowered to half-staff. And in one of the first of many shifts to come, the anthem played Friday was “God Save the King.”

The impact of Elizabeth’s loss will be unpredictable for Britain. She helped stabilize and modernize the monarchy across decades of enormous social change, but its relevance in the 21st century has often been called into question. The public’s abiding affection for the queen had helped sustain support for the monarchy during the family scandals, but Charles is nowhere near as popular.

While Elizabeth’s death portends a monumental shift, day-to-day life in Britain went on Friday, with children in school and adults at work and facing concerns about soaring prices.

Her passing unearthed conflicting emotions. For some, Elizabeth was a queen whose coronation glittered with shards of a stunning 3,106-carat diamond pulled from grim southern African mines, a monarch who inherited an empire they resented.

The changing of the guard also comes at a fraught moment for Britain — with the country facing recession and just after a brand-new prime minister took the reins. 

Ms. Truss, appointed by the queen 48 hours earlier, called Elizabeth “the rock on which modern Britain was built.”

King Charles called his mother’s death “a moment of the greatest sadness for me and all members of my family,” adding: “I know her loss will be deeply felt throughout the country, the Realms and the Commonwealth, and by countless people around the world.”

Some people gathered outside Buckingham Palace wept when officials carried a notice confirming the queen’s death to the wrought-iron gates on Thursday. Hundreds gathered in the rain, and mourners laid heaps of colorful bouquets at the gates.