- Popocatepetl is rumbling continuously, spewing gas and glowing rocks.

- The volcano, located 34 miles from Mexico City, has a long history of activity.

- Concerns are growing for further eruptions that could dump huge quantities of ash over one of the world's largest metropolitan areas.

Mexico's Popocatepetl volcano has rumbled continuously and spewed gases and glowing rocks to almost one mile (one kilometer) beyond its crater, authorities said Friday.

Popocatepetl is located about 34 miles (55 kilometers) east of the capital, Mexico City. More than 30 million people live within sight of the volcano.

In an increase of activity the volcano registered "62 expulsions of medium intensity, with the emission of water vapor, gas, ashes and glowing rocks," between Thursday night and Friday, said a statement from the National Center of Disaster Prevention.

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Authorities raised the alert level Monday to five on a seven-point scale, extending a security radius around the 5.452-meter (17,887-feet) volcano but stopping short of starting evacuations from nearby communities.

Concerns are growing that should a larger eruption occur huge quantities of ash could be dumped on one of the world's largest metropolitan areas, potentially causing chaos for Mexico City's busy air traffic.

Residents in the nearby town of Santiago Xalitzintla said the volcano was now constantly rumbling.

"There was a strong humming sound all night… it's roaring," said Alvaro Perez.

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Another resident said her family was scared of what might happen next.

"My smallest son, who is four years old, was woken up by the roar during the night," said Sofia Lopez. "'Mum, are we leaving now?' he asked me. I told him that it was OK, but the truth is that we're very scared."

NOAA's Geostationary Operational Environmental Satellite, GOES-13, captures visible and infrared images of weather over the eastern U.S. every 15 minutes, and spotted an ash and gas cloud streaming from the volcano over several hours during the morning of April 18, 2012.

The short, four second black and white video covers several hours and shows the volcano's ash blowing to the east, and over the central state of Puebla.

On the ground, officials in Puebla have prepared temporary shelters for possible evacuations and locals were wearing face masks to protect their lungs from ashes in a populous area around the volcano.

Popocatepetl, Mexico's second highest peak, means "smoking mountain" in the indigenous Nahuatl language.

After moderate activity during most of the 20th Century, the towering mountain registered more intense rumblings from 1994, with the strongest in December 2000 when nearby communities were evacuated.