Authorities in Mexico have raised the alert level for the Popocatepetl volcano due to increasing activity. It is now step five of a seven-level warning scale.
The lava dome of Popocatepetl, located in the Mexican states of Mexico, Puebla and Morelos some 40 miles southeast of the capital Mexico City, is expanding, according to Mexico's National Centre for Disaster Prevention.
The 5,450-meter volcano has also recently been spewing fragments of incandescent rock, as well as water vapour and ash.
Several schools around the volcano were closed as a precaution, with evacuation shelters also being prepared.
The volcano could experience "significant explosions of growing intensity that hurl incandescent rocks significant distances," large ash showers and possible flows of mud and molten rocks down the volcano's flanks, the centre said.
The surrounding area has been closed to visitors and people were urged to stay at least seven miles from the crater, according to the centre. Residents were also advised to clear ash from weak rooftops and to cover their mouths to avoid inhaling it.
The centre raised the alert level to yellow phase three from yellow phase two, indicating possible magma expulsion and explosions of increasing intensity. The next stage is red alert, which, presumably, would prompt evacuations to begin.
Jesus Hernandez Mendoza, head of the Regional State Civil Protection Institute, said the recent seismic activity was within scenarios provided by Mexico's Scientific Advisory Board and is not yet cause for alarm.
Officials said the alert could remain in place for weeks or months - until the volcano's activity diminished.
Known as "El Popo," the volcano staged its most violent eruption in 1,200 years on 18 December, 2000, forcing the evacuation of tens of thousands of people from nearby communities.