Mexico worked Wednesday to identify charred bodies left by an explosion that killed at least 31 people at its biggest fireworks market, as authorities investigated what caused the multi-colored salvo of destruction.

Forensic experts are carrying out genetic analyses to identify the badly burned remains from the Tuesday blast, with just 13 victims identified so far, said state prosecutor Alejandro Gomez.

Eight victims were minors, he told TV network Televisa.

Another 72 people were injured in the explosion. Forty-seven remained in hospital Wednesday, many with severe burns covering their bodies.

Three badly burned children were due to be transferred to a specialized hospital in Galveston, Texas.

Rescue workers were still searching for bodies -- or survivors -- in the smoldering wreckage of the San Pablito market in the Mexico City suburb of Tultepec.

At the time of the blast, it was packed with customers buying pyrotechnics for traditional end-of-year festivities.

Christmas and New Year parties in many Latin American countries often wrap up with a fireworks free-for-all.

But the holiday season took a horrific turn.

"I thought we were all going to die," said Luis Hernandez, 26, at the shop where he has assembled fireworks for the past 12 years.

"People were running. Children were shouting. Lots of burned people were walking around, not knowing what to do. And we didn't know what to do either, because we were afraid the explosions would start again."

Other survivors described hellish scenes of people on fire, including children, running from the market as blue, red and white explosions lit up the sky.

The remains of the market looked like something from a post-apocalyptic film, with little left standing in the smoldering ruins.

Hundreds of heavily armed police guarded the entrances, which were sealed off with yellow police tape.

The main one was still crowned with a giant sign reading "Visit! Open all year. We have full safety measures."

Fire crews struggled for three hours before bringing the blaze under control.

Officials said crews had to wait for all the fireworks to finish exploding before they could extinguish the flames.

Small explosions continued to startle locals through the night. Authorities said they were controlled blasts to eliminate remaining gunpowder.

In some areas, emergency workers were gently probing for survivors under heaps of charred and twisted roofing material.

Homes and vehicles nearby were also severely damaged.

"I thought my house had collapsed," said resident Artemio Aguilar as he cleaned up the firework remains littering his block.

The military, which is in charge of issuing fireworks sales permits, was deployed to help emergency crews.

Ambulances, fire trucks, police vehicles and army trucks all crowded the sprawling blast area.

The attorney general's office has opened an investigation into the cause of the blast.

State and federal investigators were combing through the burnt remains of the market.

Some witnesses said a rocket that went off at one seller's stall triggered the chain reaction.

"We cannot verify that theory, since the person working at the stall in question is unfortunately deceased," investigators said in a statement.

Other locals told AFP the blast was caused by a "bomb," a pyrotechnic product the size of a tennis ball that lights up the sky in colorful circles.

Gomez, the investigating prosecutor, said the probe was only just beginning.

"I have no theories for now," he said. "Our priority has been to attend to the injured, remove the bodies and deal with the emergency."

He said forensic photographers and explosives experts would analyze the scene as necessary in the coming days.

"Fireworks are a risk. It's inevitable. If a rocket goes off, it ignites the others. Security measures are worthless," said resident Roberto Cortez, a 48-year-old mason.

The market had already been rocked by two explosions in the past: in September 2005 ahead of the Independence Day holiday, and again the following year.

Both incidents left dozens of injured, but no fatalities.