Gabon said the fire lasted for nearly three hours.
Police were unable to say why the firecrackers caught fire.
The remains of the victims were found inside a bathroom where they had tried to escape from the blaze, said Eliseo dela Paz, chief superintendent with the provincial police.
A television station reported that the store did not have a permit to sell firecrackers, and Cobillo said emergency exits were locked.
Police are attempting to find the store's owner.
In the Philippines many Filipinos celebrate Christmas and New Year by exploding firecrackers, causing dozens of injuries, fires and deaths each year.