Mexico is celebrating the Day of the Dead this weekend with colourful festivities in which families honour and remember dead loved ones.
"I have ordered a thorough and transparent investigation to clarify the causes of the accident," Alfonso Durazo, governor of the state of Sonora home to the city, said in a video on social media, on Saturday, adding that children were among the victims.
Most of the deaths appeared to have been from inhalation of toxic gases, said Gustavo Salas, the state's attorney general, citing its forensic medical service.
"My heartfelt condolences to the families and loved ones of those who lost their lives," President Claudia Sheinbaum said in a post on X, adding that she had directed support teams to be sent to help victims' families and the injured.
Sonora's Red Cross said its 40 staff and 10 ambulances joined in the effort, making six trips to the hospital.
The cause of the fire, now doused, was still unclear, though some media blamed an electrical failure. City officials said the store, part of popular discount chain Waldo's, was not the target of an attack.
The chief of the city's firefighters said it was still being investigated whether there was an explosion.
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