A host of European leaders are self-isolating after the French President, Emmanuel Macron, tested positive for Covid-19.
Mr Macron, 42, will self-isolate for seven days while working remotely, the Elysée Palace said in a statement.
The French president attended a number of high-profile events in recent days, including an EU summit.
Following his diagnosis several other European leaders, including the Spanish PM, said they would self-isolate.
"The President of the Republic has been diagnosed positive for Covid-19 today," the Elysée said on Thursday morning. The diagnosis was made following a "test performed at the onset of the first symptoms", the statement added.
The French president's wife Brigitte Macron, who is 67, is self-isolating but has no symptoms.
It is not yet known how Mr Macron caught the virus but his office said it was identifying any recent close contacts he has had.
On Tuesday President Macron hosted French parliamentary heads and on Monday members of the intergovernmental group the OECD.
Last week he, along with almost every other EU leader, attended a summit in Brussels.
Among those going into self-isolation are European Council chief Charles Michel, Spanish Prime Minister Pedro Sánchez and OECD Secretary-General Angel Gurría, all of whom met President Macron this week.
Mr Sanchez has tested negative but, like Mr Macron, will work remotely from quarantine.
Portuguese Prime Minister António Costa, 59, has cancelled all official trips, and is isolating and awaiting test results, after a working lunch in Paris with President Macron on Wednesday.
Belgian Prime Minister Alexander De Croo and Luxembourg's Prime Minister Xavier Bettel too are self-isolating following contact with the French president.
In a statement Mr Bettel wished Mr Macron a "speedy recovery".
Irish Prime Minister Micheál Martin has tested negative for Covid-19 but will limit his contacts, a spokesperson said.
French Prime Minister Jean Castex, 55, and parliamentary speaker Richard Ferrand, 58, are also self-isolating, their offices confirmed.
Mr Castex, who is not showing any symptoms and has tested negative, was due to introduce the government's Covid vaccination policy in the Senate on Thursday - now Health Minister Olivier Véran is doing it instead.
France this week ended a six-week national lockdown, replacing the measure with a curfew to help deal with soaring cases.
Mr Macron last week attended a two-day European Council heads of state summit, finishing on Friday.
However, the French president is considered to have become potentially contagious as of Monday evening, a senior EU official told the BBC.
All sanitary measures were observed during last week's meeting and the council has not been informed of any other participants testing positive, the source added.
German Chancellor Angela Merkel wore a mask at the summit and tested negative for the virus on Tuesday, German officials said after hearing the news about President Macron.
A French presidential spokeswoman confirmed that all of Mr Macron's forthcoming trips, including a scheduled visit to Lebanon on 22 December, had been cancelled.
The Elysée is doing everything to project an image of business as usual. Already President Macron is back at work, and a meeting with his finance and foreign ministers has gone ahead as planned - though with the visitors in an adjacent room.
It's being emphasised that the workings of government have already been radically adapted for Covid - with video conferences now the norm - so unless the president takes a turn for the worse no-one will notice much of a difference.
And meanwhile - as with any ordinary citizen - the trace-and-test system has kicked in, and numerous dignitaries foreign and domestic have been told the bad news that they have to self-isolate.
The message is clear: Emmanuel Macron may be the president of France - but for the purposes of the virus he is a human like any other. So he will behave according to the rules.