MEXICO CITY — Mexican authorities raised the alert level for the Popocatepetl volcano near Mexico City on Sunday morning after observing an increased level of explosive activity.

The lava dome of Popocatepetl, some 50 mi to the southeast of the capital, may expand and unleash increasingly powerful explosions of ash and lava, Mexico's National Center for Disaster Prevention said in a statement.

The alert level for the towering volcano was raised to yellow phase three from yellow phase two, on orders from the country's Interior Ministry.

It is the third-highest warning on the center's seven-step scale.

This change in activity in the 17,900-foot volcano could provoke big explosions capable of sending incandescent fragments out over considerable distances, the center added.