The fire service said three water-dropping helicopters assisted more than 40 firefighters with 19 fire engines and water trucks near the town of Lavrio, southeast of the capital. Strong winds fanned the flames through low vegetation.
The blaze did not directly threaten the arms plant, authorities said. They said about 50 refugees were moved from their nearby camp as a precaution. Another wildfire on the island of Evia was reported under partial control.
Wildfires are common during Greece's hot, arid summers. Last year, 101 people died when a blaze swept through a seaside resort east of Athens.