The Popocatepetl volcano spewed ash on swaths of Mexico City and its suburbs on Monday, leaving a thin coat of dust on streets and cars.
Ash from the volcano, which is 34 miles southeast of the capital, dropped on eight southern boroughs of the mega-city and six of its suburbs, according to the National Disasters Prevention Center.
"I had cleaned the car yesterday and today it was gray and dirty when I woke up," said Luis Carlos Carranza, a 27-year-old driver for ride-sharing app Uber, who lives near the international airport.
Activity at the volcano in central Puebla state, popularly known as the "Popo" or "Don Goyo," intensified late Sunday before returning to normal at around 3:30 am on Monday, the center said in a statement.
The explosions launched white-hot rocks as far as 1,800 feet on its northeastern slope while emitting ash and water and gas vapors.
Civil protection authorities urged residents to remove ash from roofs and streets, and put the dust in trash bags to keep it from clogging drainage systems.
Officials also advised people in the affected areas to close their windows and stay home as long as possible.
Other tips include covering their noses and mouths with a wet towel, cleaning their eyes and throats with clean water, and avoiding wearing contact lenses.
The alert level remained at Yellow Phase Two, two steps under preventive evacuations of homes.
The 12,887-foot volcano, Mexico's second highest summit, regularly spews ash but it rarely reaches the metropolitan area of 21 million people.
Maria Elena Gonzalez, a 43-year-old lawyer, was taking her two children to summer school when they noticed the dust.
"They were surprised to see the gray layer on the car and they started drawing on the windows with their fingers," she said as she cleaned her car with a wet cloth in front of her house in the borough of Alvaro Obregon. "I have to hurry to clean it. I can't go to the office like this."