As fire and emergency crews were brought in, officials evacuated 200 people from the mostly rural area south of the capital Santiago.
More than 450 square kilometers (175 square miles) were ablaze in the O'Higgins region -- an area roughly the size of Vienna or Tel Aviv.
As fire and emergency crews were brought in, officials evacuated 200 people from the mostly rural area south of the capital Santiago. Some 30 homes were affected in Cardenal Caro and Colchagua provinces, the National Emergency Office (ONEMI) said.
A local ONEMI official, Josefina Lopez, told AFP that no one was hurt but there was economic damage.
Agriculture Minister Carlos Furche told national radio the disaster was "a sort of earthquake" for the region.
President Michelle Bachelet took time out of hosting a visit by French counterpart Francois Hollande to monitor the situation and declare the state of catastrophe, which allows soldiers to be used to help battle the fire. A farming emergency was also decreed.
Bachelet said France was offering help and she was also reaching out to other countries.
Chile's National Forestry Corporation said on Friday that outside assistance was needed. Interior Minister Mario Fernandez said helicopters and planes in particular were required.