The Calbuco volcano in southern Chile has erupted twice in the space of a few hours.
The Calbuco had been dormant for decades.
Footage from the area shows a huge column of lava and ash being sent several kilometres into the air.
The Calbuco volcano is one of the most active in Chile, but there had been no sign that the volcano was about to erupt.
The authorities have declared a red alert and evacuated more than 4,000 people within a 20km (12 mile) radius.
The inhabitants of the nearby town of Ensenada - along with residents from two other smaller communities - have been ordered to evacuate their homes. The nearby town of Puerto Varas was also under a state of alert.
The nearby city of Puerto Montt - a gateway to the popular Patagonia region - has already been blanketed in a cloud of ash.
Chile has the second largest chain of volcanoes in the world after Indonesia, with around 500 that are potentially active.
It is southern Chile's second volcanic eruption in as many months. In March, the Villarrica volcano erupted in the early hours of the morning, spewing ash and lava.
Hundreds of people live within the shadow of the volcano. Interior Minister Rodrigo Penailillo called on people affected to "remain calm and stay informed".
