The Villarrica volcano, one of Chile's most active, began erupting around 3:00 am (local time), prompting authorities to declare a red alert and cancel classes in schools, the National Emergency Office said.
As sirens sounded, Chilean TV footage showed lava spilling from the volcano about 800 km south of the capital Santiago.
But hours later it seemed to have calmed down, with no visible signs of eruption. Still, President Michelle Bachelet appealed for calm and authorities blocked roads leading to the area around the volcano, which is about 2,800 meters high.