Argentina and Chile have issued an alert over increased activity at the Copahue volcano, which is discharging smoke and gas.
The BBC reports an orange volcano alert, the second highest, has been issued in both countries.
Planes flying over the southern Andes have also been warned.
The 3000m volcano is in the Neuquen province of Argentina, which borders the Biobio region of Chile.
Many residents have already left the area as a precaution. Residents who have stayed behind have been told to monitor the situation and be prepared to evacuate.
Ash has been raining down on the village of Copahue in Chile and in Caviahue and Zapala across the border.
Hundreds of flights were cancelled last year due to the eruption of Puyehue volcano in Chile.
