Dutch Crown Prince Willem-Alexander has been installed as Europe's youngest monarch after his mother, Queen Beatrix, abdicated, making way for a new generation of Dutch royals.
In a ceremony attended by future kings and queens, including Britain's Prince Charles, Willem-Alexander, 46, became the first Dutch king since 1890.
Thousands of orange-clad people gathered outside as Beatrix, 75, ended her 33-year reign by signing the act of abdication at the royal palace in Amsterdam's Dam Square.
Beatrix appeared on the balcony of the palace to greet the masses after signing the paperwork.
"I am happy and grateful to introduce to you your new king, Willem-Alexander,'' she told the cheering crowd, which chanted: "Bea bedankt" (''Thanks Bea'').
Moments later, in a symbol of the generational shift in the House of Orange-Nassau, she left the balcony and King Willem-Alexander, his wife and three daughters waved to the crowd.
"Dear mother, today you relinquished the throne. Thirty-three moving and inspiring years. We are intensely, intensely grateful to you," the new king said.
Beatrix, 75, became a mere princess again after her son took over the throne.
The king's popular Argentine-born wife became Queen Maxima and their eldest of three daughters, Catharina-Amalia, became Princess of Orange and first in line to the throne.
Willem-Alexander pledged to use his ceremonial position as head of state to help steer his country through uncertain economic times.
"I am taking the job at a time when many in the kingdom feel vulnerable and uncertain," Willem-Alexander said. "Vulnerable in their work or health. Uncertain about their income or home environment."
European Union figures released on Tuesday showed Dutch unemployment continuing to trend upward to 6.4 percent - still well below the EU average of 10.9 percent, but higher than it has been for years in the Netherlands.
More than 10,000 police were deployed in Amsterdam for the festivities, and bomb-sniffing dogs carried out security checks for the crowd on Dam Square.
Police said they had arrested 70 people since Monday, including 15 involved in a fight for a good spot to set up a flea market stall. The Dutch traditionally sell their unwanted goods on April 30, a national party usually known as Queen's Day.
Authorities have closed off Amsterdam airspace to civilian aircraft for three days and issued strict orders prohibiting the use of drones, with rooftop snipers keeping a watchful eye.
The monarchy is popular in the Netherlands, but some question the cost of the royal household and republicans are seeking to get the king's $1m tax-free salary reduced.
An anti-monarchist demonstration was held in the capital on Tuesday, with protesters dressed in white instead of orange and signs mocking Willem-Alexander.