Mexican authorities raised the alert level for the Popocatepetl volcano near to Mexico City on Monday after it started spewing red-hot fragments of rock.

The lava dome of Popocatepetl, some 50 miles (80 km) to the southeast of the capital, started to expand on Friday, Mexico's National Center for Disaster Prevention said.

This change in activity in the 5,450 meter (17,900 foot) volcano could provoke big explosions capable of sending incandescent fragments out over considerable distances, as well as ash showers, the centre said in a statement.

The centre raised the alert level to yellow phase three from yellow phase two, indicating possible magma expulsion and explosions of increasing intensity. It is the third-highest warning on the centre's seven-step scale.

Emergency services should ready evacuation teams and shelters, limit access to the area around the volcano and alert air-traffic control systems, the centre said in its statement.

Experts have noted increased activity in Popocateptl in 2012. It has spewed smoke and ash sporadically over the last few years and a major eruption in 2000 forced the evacuation of nearly 50,000 residents in three states surrounding the peak.

(Reporting by Elinor Comlay and Armando Tovar; Editor by David Brunnstrom)