Mexican authorities raised the warning level for the Popocatepetl volcano to one step below red alert, as smoke, ash and molten rock spewed into the sky posing risks to aviation and far-flung communities below.
The volcano, located in central Mexico, is considered one of the most dangerous in the world because some 25 million people live within a 100-kilometer radius.
The increased alert level to "yellow phase three" comes a day after two Mexico City airports temporarily halted operations due to falling ash.
The yellow warning means "remain alert and prepare for a possible evacuation," according to the warning system developed by Mexico's National Disaster Prevention Center.
Popocatepetl, which has not had a massive eruption in more than a millennium, became active again in 1994 and has seen periods of increased activity ever since.
