Albert II, king of a sharply divided Belgium, called on its people Saturday to stick together as he bade them a formal farewell ahead of his abdication after 20 years on the throne.

The king said that as he prepared to step down Sunday, his first wish was that Belgium, split between a Flemish-speaking north and a French south, "retains its cohesion" and builds on the gains made over the past 40 years of change.

"The country has been transformed ... in a peaceful and democratic way ... into a Federal state whose parts enjoy a large degree of autonomy," Albert said in a television broadcast on the eve of Belgium's national day.

The latest reforms will only increase this autonomy, said the king, 79.

With a difficult history and an independent state only since 1830, Belgium has struggled to accommodate the often competing demands of its main Flemish and French communities.

The drive towards autonomy has eased some tensions but there remain very strong separatist elements, especially in the Flemish north, which want even greater freedom to the point where some fear for the future of a single Belgium in elections due next year.

The king said that at a time of rapid change, it was important that political power be exercised at the most appropriate and most effective level.

He singled out for praise those politicians who were ready for "constructive compromise" and had shown "a remarkable sense of the common interest" during difficult moments.

He gave no names but on two occasions, the broadcast carried clips of current Prime Minister Elio Di Rupo who, with the king's support, took office in 2011 after polls some 18 months earlier had failed to produce a government.

"I am convinced that maintaining the cohesion of our Federal state is vital, not only for our quality of life together, which requires dialogue, but also so as to preserve the well-being of all," he said.

Amid some uncertainty whether Crown Prince Philippe is ready to take the throne, Albert said that as both king and a father, his "very dear wish" was that the people actively support the new monarch and his popular wife Mathilde.

"They make an excellent couple in the service of our country and they have my confidence," he said.

Prince Philippe, 53, said just after the king announced his abdication early this month that he was "well aware" of his responsibilities and would make a "wholehearted" effort to meet them.

Prime Minister Di Rupo pointedly said at the time that Philippe "has seriously and with a sense of responsibility prepared himself for his new functions".

King Albert II also called on Belgians to keep faith in Europe despite the continuing economic crisis, saying that many of today's problems could only be tackled at European level.

A commitment to Europe was the best way to defend core values such as "social diversity, democracy, tolerance and solidarity, the protection of the weak".

But Europe is more than just a budget project too, he said, and it must address the issues of sustainable growth, jobs for youth -- among those hardest hit by the economic slump -- and social justice.

Belgium, home to some 11 million people at the crossroads of Europe, was one of the first nations to join the forerunner of the European Union and hosts many of the EU's major institutions.

Pundits said the king's address was sober and appropriate, being neither populist or divisive as the attention now turns to Sunday's abdication and the swearing in of Philippe.

On Saturday, the tone appeared muted in Brussels with some houses flying the national flag but it is expected that the formal ceremonies Sunday will attract very large crowds.