Volcano red alert
"Authorities have overflown the volcano area and the alert is still red," said Gilda Grandon, from Onemi's BioBio unit.
"We have noted some drop in the ash plume but the alert level is maintained because a full eruption is not ruled out."
The Mining Ministry's Sernageomin geology unit has recommended careful observation of a nine-mile radius around the active crater in case of mudflows of volcanic fragments.
Officials say there is no need yet to evacuate.
The 2,967m-high Copahue last erupted in 1991. Some 20 years later, in 2001, it became highly active with blasts and gases.
A volcano in the Caulle Cordon of southern Chile erupted violently last year, forcing the cancellation of hundreds of flights and the evacuation of more than 3,500 people.