An elevated section of the Mexico City metro collapsed and sent a subway car plunging toward a busy boulevard late Monday, killing at least 23 people and injuring about 70, city officials said. Rescuers searched a car left dangling from the overpass for hours for anyone who might be trapped.

Those efforts were suspended early Tuesday, however, because of safety concerns for those working near the precariously dangling car. A crane was brought in to help shore it up. “We don’t know if they are alive,” Mayor Claudia Sheinbaum said of the people possibly trapped inside the car following one of the deadliest accidents in the city’s subway system, which is among the busiest in the world.