Footage from the area shows a huge column of lava and ash being sent several kilometres into the air.

The authorities have declared a red alert and evacuated more than 4,000 people within a 20km (12 mile) radius.

The Calbuco volcano is one of the most active in Chile, but its eruption took officials in the area by surprise.

Alejandro Verges, an emergency director for the region, said Calbuco had not been under any special form of observation.

The inhabitants of the nearby town of Ensenada - along with residents from two other smaller communities - have been ordered to evacuate their homes.

Schools in the area have been shut and some flights cancelled.

The nearby city of Puerto Montt - a gateway to the popular Patagonia region - has already been blanketed in a cloud of ash.

TV footage showed traffic jams in the city and long queues at petrol stations. The nearby town of Puerto Varas was also under a state of alert.