One person was killed and three others were seriously injured in a blast at a suspected clandestine drug laboratory in the northwestern Mexican city of Culiacan, military spokespersons said.
Four people were doing welding work inside the warehouse when an ammonia tank explosion caused the roof and walls of the building to cave in, they said.
A man identified as Juan Ramon Beltran Beltran was killed in Friday's explosion and the injured suffered severe burns, the spokespersons said.
Military personnel found flasks, lab reactors and chemical products at the scene, leading them to suspect a synthetic drug lab was housed inside, the commander of the 9th Military Zone, Gen. Marco Antonio Covarrubias, said.
A sign on the building's facade said the warehouse sold construction material.
A representative of the federal Attorney General's Office arrived at the scene at the general's request to begin the investigation.
The blast forced the evacuation of a nearby daycare facility but the 246 children and 52 employees at that establishment were unharmed, a municipal emergency management official said.
The area was cordoned off while the investigation continues.
Culiacan is the capital and largest city of Sinaloa state, the birthplace of the first generation of high-profile Mexican drug traffickers, including Joaquin "El Chapo" Guzman, the fugitive boss of the Sinaloa cartel and - according to Forbes magazine - one of the world's richest people.
Turf wars among rival drug cartels and conflict between the criminals and the security forces have claimed more than 50,000 lives in Mexico since December 2006, when newly inaugurated President Felipe Calderon militarized the struggle against the traffickers. EFE