MEXICO CITY - At least 22 people were killed after an explosion triggered a fire at a department store in Hermosillo, capital of the northern Mexican state of Sonora, local media reported Saturday.

The explosion occurred in the afternoon at a chain department store in the city center, according to the reports. Witnesses said the fire quickly spread through the building and nearby vehicles, trapping several people inside.

Rescue teams rushed to the scene to conduct search-and-rescue operations and transport the injured to local hospitals.

Preliminary investigations suggest that the fire may have been caused by smoke from a malfunctioning transformer.

Authorities in Sonora said the possibility of a terrorist attack has been ruled out.