A Yellow Level 3 alert was posted for the area around the volcano Tuesday, meaning there was a intermediate or high probability of a violent eruption, which would range from an ash cloud to a possible explosion.
Schools were shut down in the area and residents were advised to stay inside and keep their windows closed to keep out the moderate amounts of ash that have been escaping from the mountain, CNN said.
Puebla state officials earlier evacuated a 7-kilometer (4.3 mile) perimeter around the mountain.
Scientists monitoring the volcano said Tuesday they saw glowing lava inside the crater overnight and recorded a 40-minute tremor.
Popocatepetl, known as Popo, is located not far from Mexico City and has not experienced a major eruption since 2000.