Chilean authorities have ordered a mandatory evacuation of a 25-km radius around the active Copahue volcano, which straddles the border with Argentina.
The volcano, located hundreds of kilometers from capital Santiago in south-central Chile's Bio Bio region, has seen increasing seismic activity in recent weeks, but still has not erupted, authorities said.
According to the National Geological and Mining Service (Sernageomin), the volcano "is now in a process that risks turning into an eruption, for that reason we've issued a red alert," Interior Minister Andres Chadwick said on a nationally televised news conference.
Authorities estimated that about 2,240 people will be evacuated.
In neighbouring Argentina's Neuquen province, authorities declared a "yellow alert," but said evacuations were not necessary. However, school classes in Argentina's Caviahue-Copahue, home to about 900 people, were suspended.
In mid-2011, ash from a volcano in Chile's Puyehue-Cordon Caulle chain that erupted after decades lying dormant forced the sporadic cancellation of hundreds of flights, especially in neighbouring Argentina and Uruguay.