Europe will become more "assertive" on the world stage, the new head of the European Council, Charles Michel, vowed Friday as he took over from Donald Tusk.

They staged a formal handover of the job in a ceremony featuring the symbolic ringing of a bell that Tusk handed over to Michel in front of EU staff and reporters.

It was part of a wider transition in Brussels that will, from next week, also see a new European Commission - the EU's executive arm - take charge under Ursula von der Leyen.

The European Council president is tasked with representing the national leaders of EU member states who have final say over much of the bloc's business, and also chairing their regular summits.

Michel, a 43-year-old former prime minister of Belgium, hailed Tusk and his focus on maintaining European unity over the past five years as it weathered Brexit, a migration crisis, attacks by jihadists in several EU states, and financial tribulations. But, he said, the time had come for the EU to become more "confident, self-assured and assertive" globally, notably by building common defence and security structures. "We live in peace, but we must remain vigilant, very vigilant," he said.

That pledge matches ambition voiced by French President Emmanuel Macron, who argues Europe should have defence capabilities to match its economic heft.

The European Union is increasingly finding itself caught in trade tensions between ally the United States and China, having to deal with a forceful Russia, and security threats that cannot all be addressed by NATO.

"I want Europe to become the global leader of the green movement," said Michel, lining up with von der Leyen's commitment to tackle climate change.

Tusk, 62 and a former premier of Poland, was applauded by the EU Council workers for so long he asked them to stop, "because I will start to cry".

He is to become the leader of the European family of the main conservative parties across the bloc, the European People's Party, which is the biggest grouping in the European Parliament.

He said his mandate tackling a series of different crises reflected a quote by filmmaker Alfred Hitchcock, which he paraphrased as: "I want a film that starts with an earthquake and works up to a climax."

Michel, in a nod to Tusk's famous bluntness, said that while he too was "open to dialogue," he would be "perhaps more cautious with my tweets - at least at the beginning - but I will also speak out when needed".