A volcano in Ecuador that has not erupted in nearly 140 years belched a column of ash five kilometers (3 miles) high on Friday, prompting officials to raise the alert level.

The ash was preceded overnight by two small explosions from the crater, the Geophysics Institute said on Twitter.

The Cotopaxi volcano stands 5,897 meters (19,500 feet) high and is located 45 kilometers (30 miles) south of the capital Quito.

In Quito, preparations began for a million surgical masks to be handed out.

The Geophysics Institute said Cotopaxi is one of the most dangerous volcanos in the world because of the large amount of snow at its peak and because nearby areas are densely populated.

The last time it erupted was in 1877.

The government's emergency management agency raised the alert level in areas near the volcano to yellow, which is in the middle of the scale.

The Environment Ministry declared the volcano off limits to tourists. Fifteen climbers who were preparing to scale the mountain were sent home.
Authorities are monitoring the volcano closely as they decide whether to order evacuations.

Airports in Quito and in the town of Cotopaxi remained open despite the plume of ash, the civil aviation directorate said.

In the town of Machachi, 25 kilometers (16 miles) from the volcano, people started wearing surgical masks.

Brian Manzano, a hotel receptionist there, said, "when I got up, I opened the door of the hotel and saw a car covered in ash. I do not know how long it has been falling."

In Quito, a city of 2.3 million, orders have been given for a million surgical masks to be distributed, Mayor Mauricio Rodas said.

Cotopaxi is one of eight active volcanos in Ecuador and is closely monitored by scientists.