Buildings also collapsed across the neighborhood of Condesa, another fashionable district in the city constructed atop soft soil and extremely vulnerable to earthquakes. Outside, thousands and thousands stood in the streets, avenues and sidewalks, filling the popular neighborhoods with a sense of dread.

On Laredo Street, an entire eight-story apartment building had fallen into the road, leaving an enormous heap of concrete and rubble pouring into the street. At least 100 people stood atop the pile clearing it by hand, piece by piece, passing boulders and twisted steel pipes along a human chain that radiated from the heap like spokes.

The sound of shouts filled the air, men barking orders at one another. Then came a call for silence — to listen for the voices of anyone trapped inside, screaming for help.

Standing on the sidewalk, Salomón Chertorivski, the secretary of economic development for Mexico City, said he believed that 10 people were trapped inside the structure. The rumble of a backhoe digging into the building’s remains and the whir of helicopters overhead dominated. A stretcher was passed up to the top of the heap.

“Whoever isn’t helping, leave,” one worker shouted to no one in particular.

Witnesses had watched in horror as people tried to escape before the building collapsed.

“It fell straight down,” said Moises Escobar, 25, a recent college graduate. “There was a lot of smoke and dust.”

Workers continued their mad scramble to pull those from the wreckage. A man raced down Amsterdam Street, looking for tools.

“Saws, hacksaws — anything to cut wood and metal,” he screamed.

Someone returned from a nearby building with a hacksaw and handed it to him, and he prepared to sprint back to the mound.

“I work near here, but we have to help,” he said. “It’s our country.”

That collective spirit filled the disaster site, as neighbors and those passing by joined to help.