EU flags were flown at half-mast in tribute to European Parliament speaker David Sassoli, who died Tuesday aged 65, as tributes flowed in from leaders and officials from around the 27-nation bloc and beyond.

"Today is a sad day for Europe," European Commission chief Ursula von der Leyen said, referring to the Italian former journalist and longtime MEP whose 2.5-year term presiding over Europe's legislature was to end this month.

Sassoli died in the early hours of Tuesday in the hospital where he had been admitted on December 26 for what his spokesman had said was "a serious complication due to a dysfunction of the immune system".

"David Sassoli passed away at 1.15am (0015 GMT) on 11 January at the CRO in Aviano, Italy, where he was hospitalised," the spokesman, Roberto Cuillo, tweeted.

The parliament's acting speaker is now its highest-ranking vice-president, Roberta Metsola, a Maltese politician who was already tipped to succeed Sassoli.

- 'Passionate European' -

The 705-seat European Parliament is one of the more important of the EU's main institutions.

But the work of the European Council, which represents the 27 member states' governments, and of the European Commission, which serves as the EU executive, is seen as more influential outside Brussels.

Under the EU treaties, the official seat of the parliament is in the French city of Strasbourg, but its MEPs spend most of their time and do much of their work in Brussels, where they have offices and use another chamber.

While the members of the European Parliament are elected for five-year terms, the speaker usually gets a mandate for half that period under a power-sharing arrangement between the parliament's biggest political groups.

The current members took up their mandates in July 2019.

Sassoli, part of the centre-left Socialists and Democrats grouping, is expected to be replaced by Metsola, the candidate of the centre-

right European People's Party grouping. Sassoli had already indicated that he would not seek re-election.

The EU flag in front of all the bloc's institutions was lowered to half-mast on Tuesday and MEPs were to hold a minute of silence in front of their Brussels building.

Sassoli's spokesman said the date and place of the funeral would be announced later Tuesday.

Sassoli had previously been admitted to hospital in September last year for pneumonia, and before his last hospitalisation he was seen in public looking wan, his hair thinning.

EU leaders and politicians were effusive in their praise of the speaker. Many used Italian in their tributes -- mirroring Sassoli's own linguistic practice, which stood out in EU business commonly carried out in English and French.

Von der Leyen, wearing all black, said in Italian and in English that Sassoli was "a passionate European, a sincere democrat, and a good man" whose legacy was that "he wanted Europe to be more united, closer to its people, more faithful to our values".

European Council President Charles Michel tweeted in Italian, and French, that he was "sad and moved" at the news of Sassoli's passing, and remembered the speaker's "human warmth, his generosity, his amiability and his smile".

Metsola said she was "heartbroken" at his death.

Italian Prime Minister Mario Draghi issued a statement lauding Sassoli as "a man of the institutions, a profound pro-European, a passionate journalist... a symbol of balance, humanity and generosity".

He added: "His premature and sudden death is shocking."

German Chancellor Olaf Scholz said Europe "has lost a committed parliament president, Italy a savvy politician and Germany a good friend".