Monday, the alert level for those near Mexico’s Popocatepetl volcano has been raised to the third highest warning level after hot rock fragments started shooting from the mountain and a vapor cloud shot a mile into the sky.

Popocatepetl is located about 50 miles southeast of Mexico City and according to local reports the volcano had “at least seven exhalations” between Saturday and Sunday.

Mexico’s National Center for Disaster Prevention raised the alert level to yellow phase three from yellow phase two, indicating that a magma expulsion is possible and explosions’ intensity will likely increase.

Nearly 50,000 residents in three states were evacuated when Popocatepetl had a major eruption in 2000.

For now, emergency services have been told to remain at the ready to evacuate residents and control access to the area around the volcano. An air alert has also been shared with air traffic controllers.

The Popocatépetl volcano is about 17,900 feet high, and according to the U.S. Geological Survey, more than tens of millions of people reside “within view” of what is described as a very “active” and “violent” volcano.