The blast took place yesterday, on the second floor of the Dulces Blueberry factory and caused the floor to collapse, injuring people working downstairs, said factory worker Ismael Bouchet.
"I was able to help five people who walked out of the building but as soon as they were out they went into shock and fainted," he said outside the factory, which produces gummy bears, jelly beans, peach rings and other sweets.
Authorities said the cause of the blast hadn't been determined but Bouchet said a steam boiler had been installed recently in the area.
Firefighters and rescue crews continued to search the building for more victims yesterday night.
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Bouchet said people could smell acid in the area where the explosion occurred.
"Since the morning, several co-workers said there was a bad smell, that it smelled of acid and because it was a new area we thought it was normal," Bouchet said.
Photographs of workers being helped by paramedics showed people with injuries that resembled chemical burns.
Ciudad Juarez is a manufacturing hub and the assembly plants there employ many of its residents.