Tens of thousands of people gathered on the streets of Copenhagen to celebrate the accession of Denmark’s new king, Frederik X, on Sunday, just two weeks after his mother, Queen Margrethe II, made the dramatic announcement that she would abdicate.

The country’s prime minister, Mette Frederiksen, presented the new king, bareheaded and wearing a dark uniform adorned with medals and golden epaulets, to the Danish people from a balcony of Copenhagen’s Christiansborg Palace, in a move seen as underlining Denmark’s democratic character.

Large crowds of people, many of them waving small Danish flags, lined the route as King Frederik made his way to the castle by car in a motorcade as bells rang out from a nearby church.

Before the public appearance, Margrethe formally passed the monarchy to King Frederik in a televised meeting, signing her abdication papers, and, handing them over to Ms. Frederiksen, saying simply, “There.”

Margrethe’s abdication was 52 years after the monarch succeeded her father in the same palace following his death. She had been the longest-serving monarch in Europe.

In a New Year’s speech, Queen Margrethe, 83, cited her age and health as factors in her decision to step down. At the same time, she announced that her son Frederik, 55, would succeed her.

King Frederik, who is known as an easygoing, sports-loving and climate-friendly prince, was already extremely popular among Danes, who overwhelmingly support a monarchy.

Denmark’s king serves as a head of state and is responsible for signing all acts of Parliament before they become law. But legislative powers have been in the hands of elected officials since 1849.

Lars Hovbakke Sorensen, an expert on the Danish royal family, said that having the prime minister announce the new monarch was a gesture that underscored the importance of the country’s democracy.

“It means that we have a monarchy where the monarchy does not have any political power,” Mr. Hovbakke Sorensen said.

He said that no crown had been laid on the head of a Danish sovereign since 1660, when the monarchy became hereditary. Before then, the king was elected, and a member of the aristocracy crowned him.

On Sunday, King Frederik stood on the balcony alongside his wife, Queen Mary, 51. The queen, who is originally from Australia, is hugely popular in Denmark, admired for her sense of personal style and her commitment to sustainability and women’s rights. The couple met at a bar in Sydney during the 2000 Olympics in what became known as a fairy-tale encounter.

(Years later in Australia, Frederik was turned away from a bar for a lack of ID.)

Queen Margrethe, known for her artwork, her chain smoking and her charisma, had previously said that she would “stay on the throne until I drop,” but she said that a recent back surgery had made her consider handing over responsibility.

In 2022, she stripped four grandchildren of royal titles to free them of the responsibilities that would come with their roles. The decision upset family members, leading her to issue an apology.

Mr. Hovbakke Sorensen said that next week, King Frederik would attend a Mass in Aarhus, Denmark’s second largest city, to show the country that he cares for the whole nation, and not only the capital city.