Mexican leaders vow to find who is responsible for the deadly explosion at a crowded fireworks market. Witness video captured Tuesday’s massive chain-reaction blast that killed at least 31 people and injured 72 others. Three injured children are being sent to Galveston, Texas to be treated for their burns.

The explosion leveled the fireworks market in Tultepec. The San Pablito Market was especially busy Tuesday as shoppers stocked up on fireworks for holiday celebrations. But the market has a history of trouble – it’s been the scene of at least two previous explosions, but this is the first one to turn deadly, reports CBS News correspondent Mireya Villarreal.

The series of massive explosions sent huge clouds of smoke into the sky.

The market was filled with 300 vendors, all selling fireworks, leading to a powerful chain-reaction of uncontrolled blasts. One person used a cell phone to capture the chaos as crowds scattered in the wake of the destruction.

Federico Juarez, a witness, said people were running as pieces of concrete and brick started falling all over the street.

Search efforts began as the smoke cleared. Crews worked through piles of twisted metal, heavy rubble and scorched wood to find any victims still alive.

Tultepec is considered Mexico’s fireworks capital, producing 80 percent of the pyrotechnics used around the country. And it hosts a popular festival every year.

But the city is no stranger to fires caused by fireworks. In 2005, a series of explosions ripped through the market, destroying hundreds of stalls. A similar incident occurred a year later.

Setting off fireworks is a traditional way to celebrate the Christmas and New Year’s holidays here. According to Tultepec’s mayor, the market was especially well-stocked Tuesday because of the high demand.

Gabriel Maldonado, general director of Coacalco municipality government, said it’s difficult to assess the damage. He called the situation “very grave” and confirmed almost the entire fireworks market was lost.

The governor of Mexico State said the country is in mourning.

The city’s mayor said the manufacture and sale of fireworks is a vital part of the local economy. He said the industry is regulated by law and heavily supervised.