A blast ripped through a street in the busy Latin Quarter of central Paris on Wednesday, causing the facade of a design school popular with foreign students to collapse, blowing out windows and starting a huge blaze.
At least 16 people were injured, including seven who are in a critical condition.
The Paris prosecutor's office said it was too early to say what caused the blast.
But the local deputy mayor, Edouard Civel, referred to a gas explosion in a Twitter post and witnesses told BFM TV there had been a strong smell of gas moments before the blast.
Television images showed rubble from the Paris American Academy strewn across the Rue Saint-Jacques and smoke rising from at least two nearby buildings that were ablaze.
More than 200 firefighters were involved in the emergency response. Paris police chief Laurent Nunez said later that the blaze had been brought under control.
Rue Saint-Jacques in the 5th arrondissement of central Paris leads from the Notre-Dame de Paris Cathedral to the Sorbonne University and the Val de Grace military hospital and is a few blocks from the popular Jardin du Luxembourg.
The area is usually packed with tourists and foreign students in the early summer.
Hopes grew on Friday for peace between Iran and the US after President Donald Trump said a deal could be signed as soon as this weekend, even as Tehran said it had not made a final decision on a pact.
Ukraine and Russia exchanged overnight drone strikes into early Friday, with Ukraine targeting a major oil processing and petrochemical region while Russia attacked railway stations and electrical substations.
Authorities in Afghanistan's western city of Herat arrested at least 30 women, accusing them of violating dress rules imposed by the Taliban government, the UN agency for women's rights said, but added that some were later released.
US President Donald Trump called off plans for renewed military strikes on Iran at the last minute on Thursday, saying negotiations with Tehran had advanced to the highest levels of Iran's leadership and had been approved by a broad coalition of regional powers.