The blast took place on Sunday morning in a residential building in Premia de Mar, north of Barcelona.
Catalonia’s Minister of Home Affairs Jordi Jané said a team of firefighters and police were still examining whether it was “accidental or not”.
Town mayor Miquel Buch said when such a large explosion occurs, officials must check “if it was an accident, or had a criminal origin”.
There were also indicators that it could have been a gas explosion.
Of the 17 injured, one man sustained burns over 30% of his body and is in a serious condition alongside two others.