A cluster of volcanoes known as the Nevados de Chillan in southern Chile could erupt within "days or weeks," according to the country's national emergency office.
The office, Onemi, issued an orange alert for risk of eruption, the second most serious alert for volcanoes, in an advisory late Monday. The agency had previously warned that the complex could erupt within "weeks or months."
Activity in the cluster of volcanoes, 380 kilometers (235 miles) south of Santiago in the Andes mountains, has increased in recent months. The biggest eruption in the cluster, with 17 craters, occurred in 1973.
The nearest towns are located in the western area of the Nevados de Chillan, including popular ski resorts. Chile's military stands ready to assist evacuations in the event of an eruption.
Chile has the second largest and most active volcanic chain in the world, behind Indonesia.