A powerful plume of steam and ash rose from the Popocatepetl volcano in central Mexico on Tuesday, prompting local schools to cancel classes and emergency teams to prepare for evacuations.
The volcano's lava dome started to expand on Friday, suggesting fresh magma may be pushing upwards. It spewed red-hot fragments and lightly dusted cars and streets in some small towns in the state of Puebla, television images showed.
Popocatepetl, which lies some 50 miles (80 km) to the southeast of Mexico City, pumped out a cloud of hot air and particles in an emission lasting about 20 minutes on Tuesday.
It sounded like a loud cauldron releasing steam, said Reuters cameraman Roberto Ramirez.
Schools in at least five small towns near the volcano called off classes after Mexico's National Center for Disaster Prevention raised the alert level for the 5,450-meter (17,900-foot) Popocatepetl late on Monday.
Carlos Gutierrez, head of operations at the centre, told Reuters that the current alert could remains for several weeks or months until the activity decreases.
The volcano, known by locals as El Popo or Don Goyo, is clearly visible from the capital on a clear day.
For locals in San Pedro Benito Juarez, a small town with population of just over 4,000 on the flanks of the volcano, people were still able to move about as usual on Tuesday.
For the elderly, this is normal. Whatever the volcano wants to do is fine. But younger people, like myself, are always alert, said Jaime Romero, a construction worker in San Pedro.
Emergency crews, which readied locals for potential evacuations, patrolled the area on Tuesday.
The volcano has spewed smoke and ash sporadically over the last few years. A major eruption in 2000 forced the evacuation of nearly 50,000 residents in three states surrounding the peak.
Every March, an indigenous leader from the area leads a celebration to honour Popocatepetl, bringing food, incense and music offerings as the agricultural season kicks off.
(Additional reporting by Liz Diaz; Writing by Cyntia Barrera Diaz; Editing by Cynthia Osterman)