(CNN) -- Mexico's Popocatepetl volcano rumbled Saturday with explosions and expulsions of ash and gas, prompting authorities to bar people from getting close to a crater that is within sight of Mexico City and many of its 19 million residents.
The country's National Center for Disaster Prevention reported that -- following 12 "low-intensity" emissions of a small amount of water vapor and gas -- there was "an exhalation with some explosive component" around 9 a.m. (10 a.m. ET).
This was "followed by a spasmodic tremor ... with moderate to large amplitudes, which has been accompanied by a continuous emission of ... ash and water vapor," according to the government agency.
At that time, the emissions had gone at most 400 meters (1,300 feet) above Popocatepetl's crater. Ash had fallen on the towns of San Nicolas de los Ranchos and Huejotzingo, as well as the northern part of the city of Puebla.
As the day wore on, the volcanic material soared even higher. An updated government report at 2 p.m. -- three hours after the first one went out -- indicated that ash, steam and gas were spewing an average of 500 meters up into the sky.
Mexican authorities restricted access within 12 kilometers (7.5 miles) of the volcano.
Located in a national park southeast of Mexico City, Popocatepetl can be seen from there on a clear day. It is one of Mexico's highest peaks and last had a major eruption in 2000.
But there have been rumblings since then. Last April, for instance, scientists observed a continuous column of water vapor and moderate amounts of ash rising from the crater.