CHILEAN authorities have urged 2000 people living near the country's Calbuco volcano to evacuate after potentially devastating mudflows of volcanic debris were detected in a nearby river.

The mudflows were the result of two huge eruptions this week that sent ash across large swathes of southern South America.

Chilean authorities said the evacuations were precautionary but necessary because flows of volcanic mud, known as lahars, are capable of levelling anything in their path once in motion.

The area had been evacuated after the volcano first erupted on Wednesday, but many people had begun to return home even as Calbuco continued to billow lesser ejections of smoke and ash.

Authorities said the evacuees from the towns of Chamiza, Lago Chapo and Correntoso would stay at shelters in the nearby city of Puerto Montt.

The volcano, which had been dormant for four decades, sent a plume of ash about 11 miles high during Wednesday's blast.

A second, outburst came early on Thursday.