MEXICO CITY (AP) — Mexican investigators were working to determine the cause of a crash in which a tanker truck carrying more than 13,000 gallons (49,500 liters) of gas exploded on a major highway in the capital, killing at least four people and injuring 90.

The fiery crash Wednesday that burned more than two-dozen vehicles created a gruesome scene of badly burned survivors staggering in the street in tattered clothing as first responders rushed to the scene. The injured suffered second- and third-degree burns.

The tragedy drew renewed attention to the thousands of trucks that rumble through Mexico daily carrying liquid propane, which most homes and businesses rely on for cooking and heating water. Regulators said a preliminary review revealed the truck did not have up-to-date insurance allowing it to transport gas.

While Wednesday’s accident involved a large tanker, rather than the smaller ones that make residential deliveries, both have been involved in deadly crashes over the past decade.

In 2020, a double tanker carrying liquid propane flipped on a highway in the western state of Nayarit and killed 13 people when the fire spread to other vehicles.

In 2015, a leak on a smaller propane truck making a delivery at a Mexico City maternity hospital allowed gas to leak into the building and blow most of it up, killing five and injuring dozens.

“This is a horrible accident,” Mexico City Mayor Clara Brugada said at the site of the explosion Wednesday night.

Lists of the injured showed that some suffered burns over 100% of their bodies. Among those injured were a baby and a 2-year-old child.

As emergency vehicles sped by and medics attended to the injured, groups of neighbors ran helped pull burn victims from the fire and get them to safety.

The crash occurred on the highway connecting Mexico City with Puebla and in the capital’s most populous borough Iztapalapa.

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 a company official who did not want to be identified denied it was their vehicle. The company did not immediately respond to an email requesting for comment or more details.

Later Wednesday, the federal agency charged with regulating industrial safety in the hydrocarbon sector said in a statement that Silza didn’t have updated insurance paperwork required to transport gas.

Mexican President Claudia Sheinbaum expressed her condolences to families of those who died in a post on X and thanked emergency teams for their work.

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AP journalists Fabiola Sánchez and María Verza contributed to this report.