In the late afternoon, the explosion ripped through the Rue Saint-Jacques, which connects the Notre-Dame de Paris Cathedral to the Sorbonne University. At least 37 people were injured, including four who were fighting for their lives in the hospital.
According to Interior Minister Gerald Darmanin, a scent had been detected by sniffer dogs beneath the pile of masonry that had been scattered across Rue Saint-Jacques.
Darmanin told reporters at the blast site, "It is possible tonight that we will find bodies or perhaps survivors."
The explosion tore down the facade of the building that housed the Paris American Academy, a popular design school for students from other countries.
Witnesses described a massive fireball that rose several stories in height and an audible explosion.
A safety cordon around the scene was secured with assistance from soldiers.
The blast's cause cannot yet be determined, according to the Paris prosecutor's office.
But Edouard Civel, the local deputy mayor, mentioned a gas explosion in a tweet, and witnesses told BFM TV that there had been a strong gas smell just before the explosion.
Rahman Oliur, who runs a food store a few doors down the street from the American Academy, stated, "The shop shook violently, it felt like a bomb blast."
Khal Ilsey, a bartender, stated that he heard a "huge explosion" before running outside and observing a violent fire at the street's end.
RUFFERING AND FIRE The explosion took place at 4:55 p.m. (14:55 GMT), just as workers were making their way home. In the early summer, tourists and international students frequent the area, but there were no immediate signs that any foreigners were among the victims.
A few close by building were cleared. Residents were still being treated for shock by first responders more than two hours after the explosion. In the street, one woman fainted.
Laure Beccuau, the prosecutor in Paris, stated that there were early indications that the blast originated within the collapsed building. He added that the investigation would look into whether the building conditions were in violation of regulations or whether an individual had acted recklessly.
The blazes were brought under control with the help of more than 300 firefighters.
Rue Saint-Jacques connects the Val de Grace military hospital to the Latin Quarter, which has been home to numerous expatriate and French writers, musicians, and artists over the years. It is also just a few blocks away from the well-known Jardin du Luxembourg.
Monique Mosser, an art historian, said, "I was at home writing... I thought it was a bomb." She also said that the blast's shockwave had destroyed many of the windows in her building.
"A neighbor came to the door and informed me that the fire department was requesting that we leave as soon as possible. I took my phone and laptop. I never even considered taking my medication.
In the 9th arrondissement, in January 2019, an explosion caused by a gas leak killed 4 and injured 66. The Notre-Dame Cathedral caught fire in April of that year, destroying much of the roof and causing other damage before it was put out.