Popocatepetl volcano shot a plume of ash and gas about 2 1/2 miles into the air Tuesday, dropping ash on cities near this capital and delaying some flights.
A dense plume was visible over the 17,887-foot volcano at dawn Tuesday. Popocatepetl is 40 miles south of Mexico City.
Ramon Pena Melche, head of Puebla state's emergency team for the volcano, said the first sizable emission occurred at 4:10 a.m. and was followed by a larger eruption at 6:50 a.m.
He said the activity was "completely within the behavior of the volcano" and did not appear to signal a more powerful eruption.
The volcano has been closely monitored since Dec. 18, when it spewed red-hot rock in its most violent eruption in 1,200 years.
The National Center for the Prevention of Disasters said ash fell on Mexico City's southeastern suburbs.
The nation's two major airlines, Mexicana and Aeromexico, briefly suspended takeoffs from the Mexico City airport while they analyzed whether the ash could damage jet engines, said airport spokesman Jose Luis Orive.