The explosion tore through Rue Saint-Jacques, which runs from the Notre-Dame de Paris Cathedral to the Sorbonne University, late on Wednesday, injuring at least 37 people, four of whom were fighting for their lives in hospital.

Interior Minister Gerald Darmanin said sniffer dogs had picked up a scent under the mound of masonry left strewn across Rue Saint-Jacques.

"It is possible tonight that we will find bodies or perhaps survivors," Darmanin told reporters at the scene.

The blast destroyed the facade of a building housing the Paris American Academy design school popular with foreign students.

Witnesses described a deafening explosion and a giant fireball that rose several stories high.

Soldiers helped secure a safety cordon around the scene.

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.

"The shop shook violently - it felt like bomb blast," said Rahman Oliur who manages a food shop a few doors down the street from the American Academy.

Bar worker Khal Ilsey said he heard a "huge explosion" before running out and seeing a violent blaze at the end of the street.

The blast occurred at 4.55pm (1455 GMT) as workers were heading home.

The area is frequented by tourists and foreign students in the early summer but there was no immediate indication any foreigners were among the victims.

Several nearby buildings were evacuated.

More than two hours after the explosion, first responders were still treating residents for shock.

Paris Prosecutor Laure Beccuau said early indications were the blast originated inside the collapsed building.

Investigators would look into whether building conditions were in breach of regulations or if an individual had acted without due care, he said.

More than 300 firefighters were involved in bringing the blazes under control.

Rue Saint-Jacques runs through the Latin Quarter - famed as the home to many expatriate and French writers, musicians and artists over the years - to the Val de Grace military hospital and is a few blocks from the popular Jardin du Luxembourg.

"I was at home writing ... I thought it was a bomb," art historian Monique Mosser said, adding that many of the windows in her building had been blown out by the blast.

In January 2019, a gas leak caused an explosion that killed four people and injured 66 in the 9th arrondissement.

In April of that year, a fire broke out in the Notre Dame Cathedral, destroying much of the roof and causing other damage before it was extinguished.

Australian Associated Press