Slumbering giant's big bang rattles Chile and Argentina

Chilean children watch the Calbuco volcano erupt, sending up a massive mushroom-shaped ash cloud. Photo / AP

Southern Chile's Calbuco volcano has erupted for the first time in nearly half a century, spewing a giant funnel of ash 10km into the sky and prompting authorities to declare a state of emergency.

Officials ordered an evacuation for a 20km radius around the volcano and the Interior Ministry rushed in the army to temporarily take control of the province of Llanquihue and the town of Puerto Octay.

Emergency measures were also in place in neighbouring Argentina, where officials in the picturesque city of Bariloche - about 100km from the volcano - said they were expecting the arrival of ash clouds within hours and warned people to stay at home.

Puerto Montt, over the border from Bariloche and the largest Chilean city in the area, was already blanketed in a cloud of ash.

"People are very, very frightened," said Gervoy Paredes, Mayor of Puerto Montt. "The situation is pretty complicated," he added, saying reports indicated the Blanco River was flooding because of ice melt triggered by the eruption.

Airlines cancelled flights as the towering, mushroom-shaped ash cloud rose from Calbuco's snowy peak.

Schools also suspended classes in the region.

Television images showed large traffic jams and long lines at petrol stations in Puerto Montt, where a red alert was declared, along with nearby Puerto Varas.

"I would like to call on the population to remain calm and stay informed," said Interior Minister Rodrigo Penailillo. "The police have given orders and begun to evacuate."

The initial evacuation involved about 270 families, but could be expanded, officials said. Calbuco had been inactive for 43 years.

It was a "rather explosive eruption", said Gabriel Orozco, a volcanologist at the National Geology and Mines Service.

He said the 10km-high ash cloud risked collapsing, and warned: "River beds are very dangerous at the moment" because of the risk of ice and snow melting and causing floods.

-AAP