FRENCH rescue workers continued searching today for a person still missing after a powerful blast brought down a building in the Left Bank district of Paris the day before.

More than 30 people were injured by the blast, four of whom were left in a critical condition. 

Investigators were working to determine the cause of Wednesday's explosion, with a possible gas leak one of the potential causes being examined.

The blast, near the historic Val de Grace military hospital in Paris’s fifth district, demolished the facade of a building that held a private academy of design and arts.

Some of the four critically injured people suffered severe burns, said Health Minister Francois Braun.

One person feared missing has been found and police said that efforts were ongoing to locate another.

Some 270 firefighters were involved in putting out the blaze and 70 emergency vehicles were sent to the scene. 

District Mayor Florence Berthout said on French TV channel BFM: “The explosion was extremely violent.”

Jema Halbert, who owns a butcher’s shop close to the explosion site, said that after hearding a loud explosion, she went outside and “saw big flames.”

Paris prosecutor Laure Beccuau announced that an investigation had been opened into aggravated involuntary injury and whether any safety rules had been broken.