A cloud of gas leaking from a truck caused an enormous explosion under a highway overpass in Mexico City on Wednesday afternoon, injuring at least 58 people, Clara Brugada, the city’s mayor, told reporters at the scene.

Many of those hurt when the inferno erupted suffered severe burns, with at least 19 in critical condition, Ms. Brugada said.

“It is a tragic accident. The prosecutor’s office is beginning investigations to determine what happened,” Ms. Brugada said, adding that no deaths had yet been reported.

The blast engulfed nearby vehicles in flames and created chaos in Iztapalapa, a working-class community and the capital’s most populous borough, with 1.8 million people.

Videos of the aftermath showed some people walking in pain with charred clothing.

Firefighters had extinguished the fire but were still trying to control the leakage from the gas tanker, which it was estimated still contained about 20,000 liters of fuel, or about 5,300 gallons, according to Judith Rodríguez Vargas, a spokeswoman with the capital’s fire department.

Miriam Castillo contributed reporting from Mexico City.