French rescue workers searched Thursday for a person feared missing after a powerful explosion brought down a building on Paris' Left Bank, injuring at least 50 people. 

In its latest update Thursday, the Paris prosecutor's office said of the approximately 50 people hurt in the explosion and building collapse that six were in critical condition, French newspaper Le Monde reported. The blast Wednesday afternoon near the historic Val de Grace military hospital in Paris' 5th district crumpled the facade of a building that held the Paris American Academy, a private fashion and design school on the edge of the city's tourist-frequented Latin Quarter. 

As a result, a fire raged Wednesday near Rue Saint-Jacques, sending out plumes of smoke that were visible from across the city. 

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Investigators were working to determine the cause of Wednesday's explosion. A possible gas leak was one of the potential causes under investigation.

Some of the critically injured people suffered severe burns, France's Health Minister François Braun said. 

One person who was feared missing has been found. Police said efforts were ongoing Thursday to locate another person still unaccounted for.

"Among the two people who were being sought in the rubble, it turned out that one had already been admitted to hospital," the prosecutor's office said, according to Le Monde. "The search continues for the second," the office added, warning: "These figures could still change."

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"Firefighters continue to clear the rubble to search for possible victims," Emmanuel Grégoire, first deputy mayor of the capital, also said, according to French outlet BFM-TV. 

According to The Associated Press, with more than 2 million people densely packed within the city limits and historic – sometimes aging – infrastructure, Paris is no stranger to gas explosions. A January 2019 blast in the 9th district killed four people and left dozens injured.

French President Emmanuel Macron acknowledged the explosion Wednesday during the annual music festival Fete de la Musique in the courtyard of the presidential Elysee Palace in Paris.

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"Tonight we celebrate the music, but the heart is not at the party. We are thinking of all those who were hit by the explosion in Paris, of the missing persons, of the rescue forces at work," Macron said in French, according to a Google translation. 

The Associated Press contributed to this report.