TULTEPEC, Mexico >> First, emergency workers rushed in to rescue the injured after a horrific blast rocked the town of Tultepec, a place already notorious for deadly fireworks accidents.

Then, 20 minutes later, a new series of explosions erupted, killing at least four firefighters, two police officers and a civil defense worker. In all, at least 24 people died and at least 49 were injured Thursday, according to the government of the State of Mexico.

A state official told local media Friday that investigators are looking at whether first responders may have contributed to the second wave of blasts by trying to extinguish the initial blaze with water, which reacts with some chemicals used in fireworks.

“Federal and state prosecutors are carrying out investigations to determine whether the water poured to extinguish the first fire … could have reacted with some element like magnesium to propagate the fire, rather than extinguish it,” said Alejandro Ozuna, the State of Mexico interior secretary.

A fireman’s blast-damaged water truck was found at the scene of the blast.

Whatever happened, it was clear the first responders tried their best and made an enormous sacrifice.

“They wanted to save lives without knowing that the same thing was going to happen to them,” said Teresa Gonzalez, who heard the nearby blasts that began at 9:40 a.m.

Tultepec, a municipality of about 130,000 people roughly an hour’s drive north of Mexico City, is famed for small workshops that produce many of the fireworks used throughout the region — and for repeated accidents that have killed at least 70 people in less than two years.

Guadalupe Romero, another town resident, stopped short of saying the town’s fireworks industry should be shut down, because he knows so many of the area’s families depend on it.

But he said that between a nearby propane gas plant and the fireworks production, “We are sitting on a time bomb.”

“Yes, we’re scared,” said the 64-year-old merchant.

Luis Felipe Puente, head of Mexico’s civil defense agency, said the workshops that exploded were “clandestine.” But they were located within an area specifically marked out for the production of pyrotechnics. State and federal officials had promised, after earlier disasters, to impose safety restrictions in such areas.

Along the road were brightly painted buildings labelled with “danger” warnings. There was even a guard shack inside a shabby chain link fence.

The shops that blew up apparently didn’t have the required permits issued by the Mexican army to store explosive materials, but that’s the case for many of the family-based businesses.

Video images showed a massive plume of smoke rising after the explosion. Journalists arriving later found wrecked buildings and scorched ground amid a rural patch of modest homes and small farm plots.

Helicopters took the wounded to several local hospitals, and more than 300 police were dispatched to the scene.

Fiercely protective of their artisanal industry, locals resist regulation, and on Thursday some assaulted journalists recording images of the site, destroying their video memory cards.

Safety measures at such workshops and markets have been a matter of constant debate in Mexico, where festivals big and small feature rockets and bombs often at close range of spectators, and individuals set off firecrackers in the streets.

“We cannot continue to allow this kind of situation,” Puente told the Milenio news network.

At least 35 people were killed in a Dec. 20, 2016, explosion that leveled a fireworks market crowded with holiday shoppers, and government officials then promised to rebuild it better than ever.

Since then there have been several other explosions at fireworks shops around Tultepec. An accident In March 2017 killed four people. Another last month killed seven and injured eight.

Deadly fireworks explosions have occurred repeatedly elsewhere in Mexico. A 1988, a fireworks blast in Mexico City’s enormous La Merced market killed at least 68, prompting a generally ignored prohibition on the sale of fireworks in the city.

In 1999, 63 people died when an explosion of illegally stored fireworks destroyed part of the city of Celaya in Guanajuato state.

A blast at a market in the Gulf coast city of Veracruz killed 29 people in 2002. In 2013, a rocket struck a truck loaded with fireworks for a religious procession in Tlaxcala state, killing 17.

Fourteen people died — including 11 children — when a firecracker landed on pyrotechnics being stored for a religious ceremony in the Puebla state town of San Isidro in May 2017.