More than 560 firefighters have been trying to contain the fire in Torres de Paine national park, which forced the evacuation of 400 tourists.
Weather conditions are not helping, with high winds expected Sunday and Monday.
A 23-year-old tourist from Israel has been detained on suspicion he negligently allowed the fire to start.
Regional prosecutor Juan Melendez identified the person as Roter Singer, though Israel Radio later gave the first name is Rotem. Melendez said the man had acknowledged a part in negligently allowing the fire to start.
The government declared a state of emergency for the region on Friday.
The Associated Press contributed to this report.