An overpass in Mexico City's metro collapsed on Monday night, killing at least 23 people and injuring about 70, city authorities said.
Mayor Claudia Sheinbaum said 49 of the injured were hospitalised, and that seven were in serious condition and undergoing surgery.
"There are unfortunately children among the dead,'' Sheinbaum said, without specifying how many.
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,'' Sheinbaum said of the people possibly trapped inside the subway car.
The mayor earlier said a motorist had been pulled alive from a car that was trapped on the roadway below.
The overpass was about 5 metres above the road in the southside borough of Tlahuac, but the train ran above a concrete median strip, which apparently lessened the casualties among motorists on the roadway below.
Hundreds of police officers and firefighters cordoned off the scene as desperate friends and relatives of people believed to be on the trains gathered outside the security perimeter.
The accident happened on the metro's Line 12, the construction of which has been plagued by complaints and accusations of irregularities.
The Mexico City Metro, one of the largest and busiest in the world, has had several accidents since its inauguration half a century ago.
Earlier this year, one was killed and 29 injured after a fire damaged the network's control facilities.
In March of last year, a collision between two trains at the Tacubaya station left one passenger dead, injuring 41 people.
In 2015, a train that did not stop on time crashed into another at the Oceania station, injuring 12 people.