The international airport Benito Juarez of Mexico City stopped working today due to ash from the Popocatepetl volcano, which has been active for a few days.

“Due to the presence of volcanic ash, the airport stopped operating at 4.25am. We will keep you posted,” his management said in a post on Twitter.

Airport workers and airline employees have taken it upon themselves to clear the runways of the aircraft.

The Popokapetl, which means “smoking mountain” in the Nahuatl language, is about 72 kilometers southeast of the Mexican capital. It has been closely monitored by scientists for decades, gathering information from cameras and sensors.

The volcano poses a danger to the millions of people who live in the surrounding area, on its eastern edge Mexico City, which has 22 million inhabitants. Earlier this week, several neighboring towns closed schools for safety reasons due to volcanic ash.