The factory is located in the Suphan Buri province north of Bangkok and images from the site show a building that has been reduced to rubble. Nine people have been confirmed dead and two are being treated in hospital.
We are trying to identify the cause of the explosion, says the local police chief Wanchai Khaoram.
Factory fires are common in Thailand. Last year, 23 people died in an explosion at another fireworks factory in the same province.
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