A volcano in southeast of Mexico City has been spewing ash for the last week causing major concern for millions of people in the area. Authorities have warned millions of residents living in a 60-mile radius of the Popocatépetl volcano that they should prepare to evacuate in case of an eruption, especially as it has also started spewing molten rock.

Known as “El Popo,” the Popocatépetl volcano, which is the second-highest peak in Mexico at 17,797 feet, has been spewing ash since 1994 after lying dormant for decades.

Currently, the volcanic threat level from the National Civil Protection Coordination (CNPC) is at “yellow phase 3,” which notifies approximately 3 million people living in towns and villages near the volcano to prepare to leave. The ash coming from the volcano has already delayed flights in Mexico City and caused schools to close.

“In the case of Mexico City, the risk is ash fall,” tweeted Mexico City Mayor Claudia Sheinbaum. “We are prepared for that scenario, and we know what to do. Let’s stay alert.”

According to El País, the Ministry of National Defense has deployed more than 7,000 troops to the area to help. Mexico’s president Andrés Manuel López Obrador has confirmed that there have been nine evacuation routes set up in case an evacuation is necessary.

“That is pretty much just part of being an active volcano,” volcanologist Jessica Ball told The New York Times. “There’s really no cycle on a human time scale that governs which volcanoes erupt at which time.”