Authorities urged 2,000 people living near the Calbuco volcano to evacuate Friday after potentially devastating mudflows of volcanic debris were detected in a nearby river, the result of two huge eruptions this week that sent ash across large swaths of southern South America.

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

The area had been evacuated after the volcano first erupted Wednesday afternoon, but by Friday, 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.

Traffic in the area was backed up as residents tried to make their way to other towns down ash-covered roadways.

Ministro de Obras Públicas dijo que hoy estarán despejadas las vías afectadas por las cenizas del Calbuco <a href="http://t.co/7jJTce73YX">pic.twitter.com/7jJTce73YX</a> —@InformacionesCL

"I'm worried about the lava because we're right below it all," said Jorge Vargas, a farmer from a nearby town who was forced to flee to a shelter with his wife and children, leaving behind their dogs, sheep and cows.

"My children are very scared. They just want to go back home, but we can't because of the (volcanic) gases."

Eruptions could last weeks

The volcano, which had been dormant four decades, sent a plume of ash about 18 kilometres high during Wednesday's blast. A second, spectacular outburst came early Thursday, with lightning crackling through a dark sky turned reddish orange by the explosion.

The head of the National Mining and Geology Service said Friday that the volcano's eruptive process could last weeks and even months and warned that a third eruption was possible.

It's highly likely that we will have other eruptions. - Rodrigo Alvarez, National Mining and Geology Service

"What I can say for certain is that this process is not going to end now," the service's director, Rodrigo Alvarez, said. "It's highly likely that we will have other eruptions, maybe not with the same amount of energy, but with activity that can be worrisome."

People in Puerto Varas sweep volcanic ash from a home's roof. (Luis Hidalgo/Associated Press) The two mighty blasts left Ensenada a ghost town, abandoned by most of its 1,500 residents. Sitting at the foot of the volcano, the town was covered in thick soot, and some roofs collapsed under the weight of the ash.

Just about 16 kilometres from Calbuco's peak, Ensenada is within the official evacuation zone, and most residents complied. But about 30 refused to leave because of worries about their homes and animals.

Ensenada was eerily empty except for a few residents using masks against the ash and an occasional horse or dog roaming its only street.

Uruguay, Argentine flights cancelled

The 2,000-metre Calbuco, which last erupted in 1972, lies near the cities of Puerto Varas and Puerto Montt, about 1,000 kilometres south of Santiago.

Officials worried the clouds of ash could contaminate water, cause respiratory illnesses and ground more airline flights.

The Tepu River is muddied from volcanic ash. Authorities n Friday urged another 2,000 people to evacuate the region around Calbuco to avoid the path of flows of volcanic mud, known as lahars, that can level anything in their path once they are set in motion. (Luis Hidalgo/Associated Press) LATAM, Sky and other airlines said they had resumed service to and from Puerto Montt after cancelling flights over fears airborne ash could damage jet engines.

But with the coarse dust spreading over nearby countries, Argentine officials grounded flights in Buenos Aires, some 1,485 kilometres from the volcano, after a small amount of ash arrived Friday and clouded the sky.

American Airlines and Air France cancelled flights to the Argentine capital's main airport of Ezeiza while Aerolineas Argentinas grounded flights to some cities in the country's southern Patagonian provinces.

Volcanic ash has created a haze in the air that hangs over the region and has spilled into neighbouring Argentina, which had to cancel some flights. (Luis Hidalgo/Associated Press) Ash also forced the cancellation of some flights to Uruguay's capital, Montevideo.

Heavier amounts of ash covered towns closer to the volcano. Cars and streets were coated with a thick blanket of ash in Villa La Angostura, Argentina, a town about 90 kilometres northeast of Calbuco.

Weather experts said the haze from the ash would likely clear up quickly unless there was another eruption.

"It doesn't look like the wind will support a very long trail based on the current forecast," said Michael Ventrice, an operations scientist at Weather Service International.