(Updates with emergency official, government comments)
SANTIAGO, Feb 19 Chile's Chaiten volcano, which erupted spectacularly last year, spewed a vast cloud of ash on Thursday in what appeared to be a partial collapse of its cone.
Television footage showed a could of ash billowing into the sky over the town of Chaiten, which lies about six miles (10 km) from the crater.
Authorities evacuated about 160 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.
"There has been a significant resumption of activity of Chaiten volcano," Deputy Interior Minister Patricio Rosende said. "Our security team have observed an increase in the size of a column of ash and smoke, with a deformation to one side."
"That leads us to presume that there is a collapse of one of the cones," he added. "This is more proof of the imminent risk in the area. It is a time-bomb."
National emergency office Onemi said that while there was a large volume of ash, there had been none of the earth tremors or groaning sounds that accompanied activity last year.
The government insists on moving the entire town, but some residents are resisting the plan -- to the exasperation of emergency officials.
"The volcano has always been in a state of eruption (since May), that has to be made clear," an Onemi official said, asking not to be named.
"We have repeatedly said that there is a red alert and that people should not be there, and if that had been respected, then police would not be evacuating people."
A cloud of debris soared as high as 20 miles (32 km) 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. (Reporting by Monica Vargas and Simon Gardner)