Mexico City (CNN) -- Scientists recorded continuing volcanic activity Tuesday in Mexico's Popocatepetl volcano, which sits just southeast of Mexico City and its more than 19 million residents.
Local government officials and residents began taking precautions, with schools in the zone near the volcano closing Tuesday and the government advising residents to close windows and avoid the outdoors.
Activity had decreased in Popocatepetl overnight, but eight exhalations of low intensity were recorded, Mexico's National Center for the Prevention of Disasters said.
A low-amplitude tremor lasting 40 minutes early Tuesday morning was also felt, the agency said.
Officials placed the alert at Popocatepetl -- which means "Smoking Mountain" in the native Nahuatl language -- at Yellow Level 3. This means there is a probability of explosive activity of an intermediate to high scale, an eruption of lava and a spewing of ash.
A glow was visible inside the crater overnight, the agency said.
Popocatepetl is one of Mexico's highest peaks and last had a major eruption in 2000. It is located in a national park southeast of Mexico City and can be seen from there on a clear day.
Already, scientists have observed a continuous column of water vapor and moderate amounts of ash rising from the crater. Falling ash was reported in the city of Puebla, the capital of the state.
A 7-mile perimeter around the volcano has been cleared, and the Puebla state government asked residents to limit travel between cities near the volcano.
To guard against falling ash, residents should close doors and windows, cover water tanks and food and avoid outdoor activities, the government said.