On Wednesday afternoon, a massive gas explosion in downtown Paris injured at least 29 people and brought hundreds of firemen to the site.

According to Paris police director Laurent Nunez, 270 firemen were dispatched to the site in Rue Saint Jacques in the city’s fifth arrondissement and have contained the fire.

Four people were “critically injured” in the event, according to police, while officials say at least two individuals are believed to be missing under the wreckage.

The Paris prosecutor, who is probing the incident, said that early signs indicate that the gas explosion came from within the building that houses the Paris American Academy, according to CNN affiliate, BFMTV.

Laure Beccuau, who visited the scene, said investigators will be leaning on accounts from injured persons in their inquiry.

A part of the building collapsed following the blast and fire, videos show. Smoke was seen billowing from the rubble earlier on Wednesday as rescue workers attempted to tackle the blaze.

Paris American Academy, a fashion and design school, describes itself on its website as the “first bilingual design school” in the French capital

Kent State University, in the US state of Ohio, said all its students at the Paris American Academy are safe and accounted following the blast.

Locals were also stopped from returning to their homes in surrounding streets by authorities in the aftermath of the explosion.

One woman, Anne, told a CNN producer at the scene that she was inside her flat, around 500 meters (1,640 feet) from the site, when the explosion happened.

“It felt like an earthquake, the windows banged against each other,” she said.

Another woman who didn’t want to give her name and lives in a neighboring avenue told CNN that her doors slammed shut from the explosion.

The local deputy mayor Édouard Civel later explained in a tweet that the impact had been caused by a gas explosion.

Paris mayor Anne Hidalgo visited the scene later on Wednesday, writing in a tweet, “My thoughts go first of all to the victims and their close ones.”

Authorities in Paris have opened an emergency response unit to handle the aftermath of the explosion.

French Interior Minister Gerald Darmanin, currently in Nancy in eastern France for a conference, will cut short his trip and return to Paris, the interior ministry told media.