Television footage showed a could of ash billowing into the sky over the town of Chaiten, which lies about six miles from the crater.
Authorities evacuated about 100 people from the area. Most of the town's 4,500 residents were evacuated last year after the volcano, dormant for thousands of years, erupted. The government is planning to relocate the town elsewhere.
"The volcano appears to have resumed activity. ... There is a cloud of ash," Paula Narvaez, special envoy to Chaiten by President Michelle Bachelet, told local television.
"This is all very preliminary, but we think this could be due to partial collapse of the cone, which was one of the dangers."
A cloud of debris soared as high as 20 miles into the air when the volcano erupted in May and was kept aloft by the pressure of constant eruptions for weeks, covering towns in neighboring Argentina with volcanic ash.
