Residents reported roaring noises from the Popocatepetl volcano near Mexico City Tuesday after signs of increased activity prompted authorities to raise alert levels. \"We can hear the roar of the volcano. Sometimes we can feel vibrations in our legs from its force,\" said Concepcion Perez, from the town of Xalitzintla in the central state of Puebla, seven miles (12 kilometers) from the crater. Authorities raised the alert level late Monday to \"yellow phase three,\" extending a security radius around the towering, glacier-clad volcano 35 miles (55 kilometers) from the Mexican capital. Officials in Puebla prepared temporary shelters in case of evacuations. The National Disaster Prevention Center said Tuesday that activity within the volcano appeared to be diminishing, but they maintained the alert level. Popocatepetl, Mexico\'s second highest peak, means \"smoking mountain\" in the indigenous Nahuatl language.