Of the injured, four were men between the ages of 24 and 29, who were hospitalized after the explosion, which happened just prior to 7 p.m. on Thursday.
The men are in a critical condition with burns to between 50 and 80 percent of their bodies.
A nine-year-old girl was treated for cuts to her hand and a police officer was also treated for smoke inhalation.
Initially it was thought that gas canisters on the property were responsible for the incident. However,
El País reports that this was later ruled out.
Investigations now suggest that the four men were filling lighters in the basement of the shop when the explosion happened.
According to a neighbor, shortly before 7 p.m. they heard a very loud explosion on the ground floor of the building and they saw three people, with their clothing visibly burned, leaving the premises.
Another witness, Alvaro Cruz, explained that just minutes before the blast, police had been handling a fight incident in the street two blocks away. When one of these officers came to investigate the explosion, he was injured by mild smoke inhalation.
The shop, located on Calle Guabairo, spewed dense black smoke into the street. Firefighters soon extinguished any flames from the explosion and it was not necessary to evacuate any residents.
The "grow shop" sells products related to the growing and smoking of cannabis, including growing equipment, lights, cannabis seeds, rolling papers, pipes and bongs.
As cannabis is decriminalized in Spain, it is legal to grow it for private use and to smoke in the privacy of your own home. However, Spanish law prohibits the sale of cannabis (finished product) and consumption in public.
