Authorities ordered the evacuation of the 1,500 inhabitants of the nearby town of Ensenada yesterday, along with residents of two smaller communities.
The National Mining and Geology Service issued a high alert, barring access to the area around the volcano, which lies near the cities of Puerto Varas and Puerto Montt, a little more than 1,000 kilometres south of Chile's capital, Santiago.
"For us it was a surprise," said Alejandro Verges, regional emergency director of the Los Lagos region where the eruption took place. He said Calbuco wasn't under any special form of observation.
Calbuco last erupted in 1972 and is considered one of the top three most potentially dangerous among Chile's 90 active volcanos.