A state of emergency was declared on the island, which sits between the Greek mainland and the island of Crete, on Saturday.
Changing winds and rugged terrain dispersed with small communities made the fire fighting task difficult, authorities said.
“The perimeter of the fire is very large,” fire brigade spokeswoman Stavroulla Maliri told Greece’s SKAI TV.
The fire brigade had called in reinforcements from other areas. Water bombing by air halted in the evening as darkness fell.
The blaze broke out in the west of the island early on Friday, but flared again on Saturday and authorities said they ordered the evacuation of two villages as a precaution.
Late July and August traditionally sees a spike in forest and brush fires in Greece, where high temperatures contribute to tinder box conditions.
Temperatures can occasionally exceed 40 degrees Celsius (104 Fahrenheit), and there have been several heatwaves this summer.