Several European leaders rushed into isolation on Thursday after French President Emmanuel Macron tested positive for coronavirus.
Officials were trying to track down Mr Macron’s close contacts after his attendance at a EU summit last week could have put most of Europe’s heads of government at risk.
The president, 42, tested positive for the virus on Thursday morning after the “onset of the first symptoms”.
He joins leaders including US President Donald Trump, UK Prime Minister Boris Johnson and Brazil's Jair Bolsonaro, who have all contracted the virus.
Mr Macron will now be in isolation for seven days in line with the country’s health guidance, but he is “still in charge” and will run the country from the Elysee Palace.
The timing is awkward for the French leader, who is trying to handle the pandemic crisis in his own country while keeping a close eye on Brexit talks and other international issues.
All of Mr Macron’s coming trips, including a visit to Lebanon next week, have been cancelled.
He was expected to push for far-reaching political change in Lebanon after the devastating Beirut port explosion.
Mr Macron’s office said it would be business as usual despite the setback.
"He will continue to work and carry out his activities remotely," the presidency said.
Mr Macron attended an EU summit in Brussels last week and on Monday he went to a conference in Paris organised by the Organisation for Economic Co-operation and Development.
European Council president Charles Michel and Spanish Prime Minister Pedro Sanchez were both at the Paris conference and have isolated themselves.
Portuguese Prime Minister Antonio Costa has also gone into isolation and cancelled all immediate events on his agenda after having lunch with Mr Macron the day before his positive test.
Luxembourg's Prime Minister, Xavier Bettel, began isolation on Thursday pending a test result after he attended the EU summit last week.
But a German government spokeswoman said Chancellor Angela Merkel took a test a few days after the EU summit and it was negative.
French Prime Minister Jean Castex will enter isolation after contact with Mr Macron, his office said, adding that he was showing no symptoms and had tested negative.
Mr Castex needs another confirmed negative result before he can come out of isolation next week, his office said.
Mr Macron's wife Brigitte will also be in isolation but also shows no symptoms.
Fellow world leaders rushed to wish Mr Macron a quick recovery.
"Sorry to hear my friend Emmanuel Macron has tested positive for coronavirus," tweeted Mr Johnson, who has locked horns with Mr Macron in recent months over the Brexit talks.
"We are all wishing you a speedy recovery.
EU Commission President Ursula von der Leyen said she was with Mr Macron "with all my heart".
"We are going to defeat this pandemic together," Ms von der Leyen said. "We will continue to work hand in hand to immunise and protect our citizens."
Russian President Vladimir Putin said he learnt of Mr Macron’s positive test "with alarm" and wished the French leader a "speedy recovery and good health for many years to come".
Mr Macron had repeatedly urged caution against the spread of the virus and in public always wears a face mask covering his mouth and nose.
France this week eased restrictions imposed to battle the second wave of the coronavirus but infection rates remain high.
There is still a nationwide overnight curfew from 8pm to halt the spread of the virus while restaurants and cafes, as well as theatres and cinemas, remain closed.
More than 59,300 people have died in France since the start of the pandemic, and more than 17,000 new cases were registered on Wednesday, bringing concern as people shop and travel before the Christmas holidays.
Like other EU countries, France is pinning its hopes on a vaccine.
Mr Castex said on Wednesday that the country would receive 1.16 million doses by the end of the year.