The fire has burned through 2,500 hectares of forest, sending plumes of smoke into the sky and blocking roads and train lines.
"We already know that the fire was intentional," said the Galician Rural Area Leader, Jose Gonzalez. "The person who started the fire knew perfectly well it could cause a lot of damage."
"We have to react together to against these fiends," Gonzalez added.
Gonzalez said teams of emergency services workers were battling the blaze, aided by firefighting aircraft and Spain's military emergency unit.
Hot weather and low humidity have so far hampered efforts to put out the blaze.