Officials in the region surrounding the Popocatepetl volcano are on heightened alert due to a small earthquake and increasing emissions from the volcano.

The alert level has been raised to Yellow-3, the third highest level on the country’s seven-stage warning scale.

The National Disaster Prevention Center says the volcano is having “exhalations” every hour with clouds so dense they are unable to determine if the mountain is spewing ash.

In addition to the 42 “low-intensive exhalations”, there had been six registered explosions and an earthquake registering 2.5 on the Richter Scale. A lava dome of over 800 feet wide and over 65 feet thick has been measured by scientists.

A radius of 7.5 miles around the volcano has been sealed off by officials. Puebla International Airport is suffering periodic shutdowns because of ash from the volcano.

Scientists are concerned the earthquake was a sign that the mountain is about to erupt.