Before signing a legislative act in the royal palace to step down, Albert thanked his wife, who wiped away tears, and said his son had all the qualities to serve the country well.

"Philippe, you have the heart and the intelligence to serve our country very well. You and your dear wife Mathilde have all our confidence," he said. "My final recommendation to all those gathered here is to work without rest in keeping Belgium together."

Philippe returned to the subject in his address to parliament, saying Belgium's richness lay in its diversity.

Philippe is the seventh king of the 183-year-old country, which is split across the middle. Many Dutch speakers seek greater autonomy for Flanders in the north and are wary of a monarchy seen to be rooted in the once powerful, but now poorer French-speaking Wallonia in the south.

"One king, two nations" was a headline in the French language business daily .

Outside the palace, a crowd gathered in festive mood, but in scorching heat that caused some to faint. Many shouted "Vive le roi" and waved flags when Philippe and Mathilde arrived on the balcony.

"The new king is a bit of history. That doesn't happen very often so we wanted to be here," said Xavier De Graef from French-speaking Liege, clad in a Belgian soccer shirt, a flag and a wig in the red, yellow and black of the Belgian tricolour.

"I am a fan of the royal family," said Cindy van Merheulen, 34, from Limburg in Flanders. "I want to welcome Philippe. Nearly all Belgians love the king. The problem is that those who are against shout louder."

Some of those dissenting voices were present, including the N-VA party that wants Dutch-speaking Flanders to break away from Belgium and favours a republic. "It leaves me cold. It doesn't make the hairs on my arm stand up. This is part of my job as a lawmaker. Otherwise it just passes me by," said Jan Jambon, its parliamentary chief.

The party has been vocal in recent weeks about the need to reform the monarchy but said it would not disturb yesterday's pageantry. Far-right separatists Vlaams Belang said they would not attend the swearing in, but planned no protests.

Michiel Descheemaeker, 21, a student who with friends was dressed in medieval costume, said he had come to protest against monarchies in general. "Kings belong in fairy tales and that's the only place," he said.

Fewer than half of the people in Flanders believe Philippe will be a good king compared with two-thirds in Wallonia, according to an opinion poll.

Belgian kings do plenty of handshaking and ribbon-cutting, but also appoint mediators and potential government heads to steer coalition talks after elections, no small task in Belgium.

The Netherlands stripped its monarchs of involvement in politics last year. Queen Beatrix also abdicated for son Willem-Alexander to become king.

Philippe's investiture was tagged onto festivities already planned for July 21, which is Belgium's national day and also marked 20 years of Albert's reign.

The government, mindful of budget savings it has forced on the public, said this should help cap costs. Even royalist Belgians feel they know little about Philippe, who has appeared reserved in public, in contrast to his more outgoing father.

That included Brigitte Kittel, from the 75,000-strong German-speaking community. "People in the German community like the king a lot," she said. "We're good Belgians. I don't know what to think of the new king yet, I know too little about him."

ABDICATIONS

: Edward VIII was forced to abdicate after only months in power on December 12, 1936, in order to marry divorced American Wallis Simpson, thus avoiding a major constitutional crisis.

Michael I was forced to abdicate by the communists in December 1947.

Victor-Emmanuel III, king since 1900, abdicated on May 9, 1946, because of his collaboration with the regime of dictator Benito Mussolini.

King Leopold III, on the throne since 1934 but controversial because of some of his actions during the second world war, was forced to abdicate on July 16, 1951, to avoid the possibility of major civil unrest after his return following six years in exile.

King Farouk I abdicated in July 1952 during the revolution led by Colonel Gamal Abdul Nasser, 16 years after his accession to the throne.

Grand Duke Jean abdicated on October 7, 2000, after a 36-year reign. His elder son, Henri, took his place.

Norodom Sihanouk, 81, abdicated on October 7, 2004, after being treated in Beijing for cancer. Sihanouk, who came to the throne for the first time in 1941, had already abdicated in 1955, in favour of his father, before again becoming constitutional monarch in 1993.

Queen Beatrix, 75, abdicated on April 30, 2013, in favour of her son Willem-Alexander, after a 33-year reign. Beatrix took over the throne on April 30, 1980, when her mother, queen Juliana, abdicated on her 71st birthday. Juliana took the throne in September 1948 after her mother abdicated.

Prince Hans-Adam II handed over management of the principality's affairs to his eldest son, Hereditary Prince Alois, on August 15, 2004.