MEXICO CITY — They arrived alone, in pairs or in groups. Some brought supplies others might need: water, blankets, medicine, tools. Others came with nothing more than able hands and a sense of purpose.

And as midnight neared on Tuesday — hours after a powerful, deadly earthquake struck central Mexico — Parque España, the verdant refuge of dog-walkers and young lovers in the Condesa neighborhood of the capital, had become the venue for something else: a frenetic, impromptu relief center, where hundreds of volunteers, under the leadership of nobody in particular, had created an emergency distribution point for food and supplies.

“It’s very characteristic of the Mexican people: We stand together,” said Christian Piñeiro, 21, a medical student, who was helping a team of doctors hand out medication. Behind him, in the darkness, supplies were being frantically passed along bucket lines of volunteers that snaked from one side of the park to the other.

“Independent of the fact that there are gangs and crime,” Mr. Piñeiro continued, “the people unify against adversity.”

The earthquake killed more than 200 people in several states, flattened dozens of buildings in Mexico City alone and damaged thousands of others. Among the dead were more than two-dozen school children. The quake, which came two weeks after another devastating temblor off the country’s southern coast, was centered about 100 miles from the capital and was followed by at least 11 aftershocks.

Millions of people were left without electricity, and President Enrique Peña Nieto said emergency workers were being sent to affected areas.

Throughout much of Mexico City on Tuesday, nightfall brought an eerie quietude, as businesses closed early and people sought the succor of their families at home. But in the hardest hit neighborhoods, the landscape was different: blocks cast in darkness from power failures were punctuated by nodes of intense activity.

On another block in Condesa, a traffic circle had been converted into a small, noisy redistribution point. Trucks, cars, motorcycles arrived, a couple every minute, to drop off supplies, which were sorted, repackaged and sent back out into the city.