Rescue workers look at fellow workers searching for people under the rubble of a collapsed building after an earthquake hit Mexico City, Mexico September 19, 2017. (Carlos Jasso/Reuters)

The seven-story apartment building had just flattened into a layer-cake of concrete.

Cirilo Cortez Alta, who lived on the ground floor and worked as a janitor, had been outside when the earthquake started after 1 p.m. on Tuesday afternoon. But he believed his 17-year-old daughter, Anayeli Juarez Hernandez, was still inside on the fifth floor, where she worked as a maid. He had frantically called her phone but received no answer.

In the throng of hundreds of volunteers frantically picking through the rubble, amid the blare of shouting and ambulance sirens and the rumble of dump trucks, Cortez stood silently, staring at what had been his home, with no idea whether his daughter was dead or alive.

"This is a tragedy," he said.

The massive 7.1-magnitude earthquake that killed more than 200 people also knocked down dozens of buildings, including many in densely packed neighborhoods of Mexico City, converting whole sections of the city into a frantic mass-rescue effort. Along one block of Escocia Street in the Colonia del Valle neighborhood, two multistory apartment buildings collapsed, with an unknown number of people trapped inside.

Residents flocked to the wreckage, using whatever tools they could find, most often their bare hands, to clear the rubble in the hopes of finding survivors. Every few minutes, someone would scream "silencio" to try to quiet the crowd in the hope of hearing voices amid the downed buildings, but shouting and sirens soon returned.

When medical workers carried bodies out on a stretcher — it was hard to tell if they were dead or alive — the crowd would clap and cheer.

Soldiers, rescuers and people work at a collapsed building after an earthquake in Mexico City, Mexico September 19, 2017. (Ginnette Riquelme/Reuters)

In the first hours after the quake, the response came from all corners: volunteer medical workers, police, firemen, Marines — whoever was nearby. Residents by the hundreds rushed to pick up chunks of concrete in the air clogged with dust. Lines formed spontaneously to pass buckets, crates, plastic barrels, shopping carts, wheelbarrows — whatever receptacle could be found — to be filled with rubble and then shuttled back through the sea of hands to waiting trucks.

Down the street, residents formed blocks-long lines to pass water, shovels and surgical masks into the areas with the worst damage. At a nearby clinic, more than a dozen hospital beds were placed in the patio as a triage center for the wounded.

"This is a tragedy and everyone who can is helping," said one man with a surgical mask over his mouth and sweat pouring down his face, before he rushed back into the fray.

In the chaos, authorities sought to control the crowd while they pursued the rescue.

"You guys organize this, you know what you're doing," a Marine shouted at a Red Cross worker. "There are a thousand people here."

Outside the flattened seven-story apartment building, search and rescue teams scaled ladders up the wreckage, to try to peek through cracks in the concrete.

"Is there anyone in here?" one volunteer shouted into the building. "We are here to rescue you."

A guy in a yellow sweatshirt began scaling the collapsed facade, which tilted at a dangerous angel. As he grabbed for a handhold, chunks of concrete tumbled down to the street below.

"Aguas!"—"Watch out" — someone screamed below. "There are people under you."

Word spread that a resident named Juan Pablo lived in the building so the crowd started shouting his name.

By late afternoon, rescuers had already pulled out at least a half dozen people, some of them alive.

"We think there are more people inside," Armando del Toro, a 46-year-old volunteer paramedic said. "Nobody can go inside there. And if you start taking any pieces out, it could all come crashing down."

Del Toro remembered jumping into rescue-mode on the same day 32 years ago, when another devastating earthquake struck Mexico City in 1985.

"Right now we are going through the exact same thing," he said.

Rescue Services search for victims under the debris of a building that collapsed after a 7.1 magnitude, in Mexico City, Mexico, on September 19, 2017. (Jose Mendez/EPA-EFE)