The blaze started on Wednesday evening near the village of Schinos as old branches in an olive grove caught fire.
"That area consists of mostly pine forest that has not been cleared in a while. Approximately 20,000 stremmata [5,000 acres] burned out," Chardalias said at an emergency briefing.
Fire brigades were mobilized from all across the Greek mainland to fight the blaze, according to the official. These included 265 firefighters, multiple planes and a Chinook helicopter.
"This is going to be a difficult night. We ask all residents in the greater area to remain vigilant," Chardalias said.
The official added that several settlements and two monasteries had been evacuated due to the natural disaster. An investigation was launched into potential arson.