A gas tanker truck exploded under a highway overpass in Mexico City Wednesday, sending flames and smoke billowing into the air, burning more than a dozen cars and injuring 57 people, the city's mayor said.

Mayor Clara Brugada called the explosion an “emergency” that left 19 people with grave injuries, but said no one had yet died from their injuries. Those injured were taken to hospitals across the city.

Brugada said that prosecutors were investigating the incident.

Images circulated online by authorities showed a mass of flames coming from a truck, while other videos on social media show dozens of people screaming and running from the explosion. The videos show two men whose entire bodies appeared to have suffered burns, with tattered clothing melded onto skin, as emergency vehicles sped by.

Cesar Cravioto, the government secretary of Mexico City, said the fire was "completely under control.” The fire burned 18 vehicles in total.

The gas tanker laying on its side had the logo of the energy business Silza on its side, but in a call with the Associated Press an official at the company who did not want to be identified company denied that it was their vehicle, saying they only operate in northern Mexico. The company did not immediately respond to an email requesting more details.

Brugada arrived to the scene of the explosion shortly after to accompany emergency teams, including firefighters and medics. Fire fighters were pouring water on the flames billowing from the gas tanker.

The explosion occurred on one of the most important thoroughfares flowing out of the country's capital on the way to the city of Puebla.

The city's government said the roadway would be closed until further notice.