The explosion occurred at around 2 pm local time (1200 UTC) on Wednesday at the Pirotecnia Zaragozana factory in the small Spanish town of Pinseque, sending a huge plume of smoke into the sky which could be seen for kilometers.
Locals living near Zaragozana reportedly heard the blast up to 10 km away.
Spanish fire services were unable to immediately enter the site due to a succession of smaller explosions.
According to a statement released by the regional government of Aragon, two of the six people injured in the accident had been admitted to intensive care.
Fears of more explosions
Initial police investigations into the cause of the fire were hindered due to a huge fire which raged for hours after the explosion.
Emergency services also warned local residents to stay away from the site over fears that remains of fireworks could still explode.
The 150-year-old factory employs around 40 people and exports fireworks mainly to Canada and other European countries.
According to Spanish newspaper “El Pais,” accidents at Spanish fireworks factories have claimed more than 110 lives in the last 25 years.
