SANTIAGO XALITZINTLA, Mexico >> At the edge of this town near the Popocatepetl volcano, away from the din of traffic, there was an occasional low rumble Monday, like an idling engine.

A cloud of superfine ash descended, slightly reducing visibility and coming to rest on vehicles’ windshields. For more than a week, the 17,797-foot (5,425-meter) mountain just 45 miles (about 70 kilometers) southeast of Mexico City and known affectionately as “El Popo,” has been increasingly explosive, spewing great plumes of gas, ash and incandescent rock into the air.

The activity led the Mexican government to raise the warning level and to close schools in dozens of municipalities across three states. On Monday, local, state and federal officials held drills for the possibility of evacuations.

“You hear it more at night,” said Violeta Fuentes, 39, who lives with her husband and two children, ages 9 and 12, on the outskirts of Santiago Xalitzintla. That’s also when they can see the glow from the crater. “Last night, several times it would go out one moment and then light up again.”

Fuentes said she was a bit unnerved by it “because you can see (the volcano) doesn’t want to be okay anymore.” The family worried about the impact the falling ash would have on their crops. Her father-in-law’s corn across the street was already coated in it.

The alerts and preparations, however, are old hat for residents here.

Job Amalco, a driver, said it was normal. “It doesn’t scare us. We’re spectators of what nature gives us,” he said proudly.

But anxiety was beginning to build among some.

“It’s worrisome, above all because of the children, because you don’t know if there will be an enormous explosion or a small one,” said Claudia de la Cruz, 27, who has two children ages 3 and 5.

Her husband hikes up the volcano’s flanks each day to collect firewood to make charcoal. “He says that there it sounds like the peaks are crashing down and it shakes, but he’s brave for us,” she said.

De la Cruz remembers as a girl the first time she saw the mountain glow and how back then residents had very little information. She trusts that now with a cellphone they will know in real time what is happening.

Still, the real warning residents listen for — as it has been her whole life — will be the urgent tolling of the town’s church bells. Monday they rang out as part of the drill.

There were no signs of panic Monday, but people worried about the possibility of having to evacuate, leaving homes and animals unattended. Authorities have warned people to stay out of 7.5-mile (12-kilometer) radius around the peak.

Florencio de Olarte, 69, and Plácida de Aquino, 72, recalled having to evacuate their home in the center of town twice before, years ago. On those occasions, “you could see (the volcano) was lit up, throwing out rocks,” Olarte said.

One of their children already wants them to come to Mexico City, but the couple doesn’t want to leave before authorities tell them they have to, because of their turkeys, pig and donkey. “We have animals and couldn’t leave them,” Aquino said.

“Right now there’s a lot of smoke plume and it oozes and thunders, the curtains shake,” Aquino said. But for the moment nothing more.

The volcano’s activity temporary halted flights at the capital’s two airports over the weekend.

On Monday, an ash plume extended hundreds of miles (hundreds of kilometers) to the east, stretching out over the Bay of Campeche, according to a U.S. National Oceanic and Atmospheric Administration report.

On Sunday, national Civil Defense Coordinator Laura Velázquez said in a news conference that the stoplight-style warning system for the volcano remained on yellow, but had risen to phase 3. Still, she said, “there is no risk to the population at this time.”

In this phase, large domes develop and explode in increasing intensity, launching incandescent rock into the air and pyroclastic flows down its flanks.

Velázquez said only three of the volcano’s 565 explosions since September had been big, and the current activity was not the greatest of this century. On Monday, she oversaw the drill in Santiago Xalitzintla.

“We don’t know what’s going to happen,” she said Monday. “We are prepared for any scenario.”

The Defense Department said it was ready to activate 6,500 troops if necessary. Shelters were being prepared.

Some 25 million people live within a 60-mile (100-kilometer) radius, most of those in Mexico City’s metropolitan area.

Popocatepetl came to life in 1994 after a decades-long dormancy and experienced periods of greater activity from 2000 to 2003 and 2012 to 2016.