Popocatepetl, a volcano one hour southeast of Mexico's capital, kept up its pattern of erupting every December for ten years, when it spit a plume of ash into the sky on Thursday.
"An explosion occurred at 6:53 this morning (1253 GMT)," said Ramon Pena, director of a government agency that monitors the volcano, Popocatepetl Operating Plan.
The plume of ash shot five kilometers (three miles) into the sky, raining ash on villages north of the volcano. No alert was sounded, however.
The volcano is 60 kilometers (37 miles) outside Mexico City. The army is permanently stationed there and the public is barred within 12 kilometers (seven miles) of the crater.
The volcano has been increasingly active in the month of December over the last ten years.
At 5,452 meters (17,887 feet) Popocatepetl, or "Don Goyo" as it is popularly known in Mexico, straddles the states of Mexico, Pueblo and Morelos in central Mexico. It first erupted 23,000 years ago.
