People clear rubble after an earthquake hit Mexico City, Mexico, Sept 19, 2017. [Photo/Agencies]

She wore a paper face mask and her hands were still dusty from having joined a rescue brigade to clear rubble from a building that fell in a cloud of dust before her eyes, about 15 minutes after the quake.

Morales said she was in a taxi when the quake struck, and she got out and sat on a sidewalk to try to recover from the scare. Then, just a few yards away, the three-story building fell.

A dust-covered Carlos Mendoza, 30, said that he and other volunteers had been able to pull two people alive from the ruins of a collapsed apartment building after three hours of effort.

"We saw this and came to help," he said. "It's ugly, very ugly."Alma Gonzalez was in her fourth floor apartment in the Roma neighborhood when the quake pancaked the ground floor of her building, leaving her no way out — until neighbors set up a ladder on their roof and helped her slide out a side window.

Gala Dluzhynska was taking a class with 11 other women on the second floor of a building on trendy Alvaro Obregon street when the quake struck and window and ceiling panels fell as the building began to tear apart.

She said she fell in the stairs and people began to walk over her, before someone finally pulled her up.

"There were no stairs anymore. There were rocks," she said.

They reached the bottom only to find it barred. A security guard finally came and unlocked it.

The quake sent people throughout the city fleeing from homes and offices, and many people remained in the streets for hours, fearful of returning to the structures.

Alarms blared and traffic stopped around the Angel of Independence monument on the iconic Reforma Avenue.

Electricity and cellphone service was interrupted in many areas and traffic was snarled as signal lights went dark.

The US Geological Survey said the magnitude 7.1 quake hit at 1:14 pm (2:15 pm EDT) and was centered near the Puebla state town of Raboso, about 76 miles (123 kilometers) southeast of Mexico City.

Puebla Gov. Tony Gali tweeted there were damaged buildings in the city of Cholula, including collapsed church steeples.

In Jojutla, a town in neighboring Morelos state, the town hall, a church and other buildings tumbled down, and 12 people were reported killed.

The Instituto Morelos secondary school partly collapsed in Jojutla, but school director Adelina Anzures said the earthquake drill that the school held in the morning was a boon when the real thing hit just two hours later.

"I told them that it was not a game, that we should be prepared," Anzures said of the drill. When the shaking began, children and teachers filed out rapidly and no one was hurt, she said. "It fell and everything inside was damaged."Earlier in the day, workplaces across Mexico City held earthquake readiness drills on the anniversary of the 1985 quake, a magnitude 8.0 shake that killed thousands of people and devastated large parts of the capital.