Popocatépetl is one of the most active volcanoes in Mexico. It is located on the border of the states of México, Puebla and Morelos and is more than 5400 meters high.
About 100 million people live within a radius of 25 kilometers. The warning level remained at "Yellow Phase 3" on Monday, one step away from the red alert. The ash should be removed from runways and then the situation should be reassessed, authorities say.