Doctors and psychologists waited on call as relatives made their way inside to ask for information. Outside volunteers gathered medicine and water.
Mony de Swaan, a resident who was coordinating the center by the light of cellphones, said that as many as seven people remained trapped. With the help of the building’s doorman who had escaped, he had made a list of residents in the seven-story building.
A young woman approached the table. “My mother’s name is Mari,” she told Mr. de Swaan. “On the second floor.”
He answered her gently. “She is still inside,” he said. “On the second floor, Mari, Lorna and Consuelo are still inside.”
The missing woman, María Ignacia Cruz, had traveled every day from her home in a poor suburb to look after an elderly lady, said Ms. Cruz’s husband, Alberto Arrellano Nicolas, sitting almost mute with worry. His adult daughter and son sat on a sofa, talking quietly with a psychologist as they tried to hold back their tears.
On a darkened street in the Roma Norte neighborhood, away from the commotion of relief efforts, a group of neighbors gathered on the street, sitting on chairs and blankets. The authorities had barred them from returning home because their apartment building adjoined a damaged one, putting both structures at risk.
Others in the city, however, were simply too unnerved to return home, out of fear of aftershocks or hidden damage, choosing instead to seek shelter with relatives and friends elsewhere.
The earthquake terrified Silvia Bustamante, 65, too, but she was unwilling to abandon the apartment she has called home for 40 years. So she came up with a compromise: She pitched a tent in the lobby, a few feet from the sidewalk.
“We’re traumatized,” Ms. Bustamante said as she stood outside her building, watching the traffic of relief workers. “I dread the thought of being upstairs and not being able to get down in time.”
Her block lay in darkness. The lights of skyscrapers on the city’s main Reforma Avenue less than a mile away seemed a very distant reminder of normalcy.