MEXICO CITY (AP) – 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 initially searched a car left dangling from the overpass 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 for the city’s subway system, which is among the busiest in the world.

Earlier Ms. Sheinbaum said someone had been pulled alive from a car that was trapped on the road below. She said 49 of the injured were hospitalized, and that seven were in serious condition and undergoing surgery.

“There are unfortunately children among the dead,” Ms. Sheinbaum said, without specifying how many.

The overpass was about 16 feet above the road in the borough of Tlahuac, but the train ran above a concrete median strip, which apparently lessened the casualties among motorists on the road below.

“A support beam gave way” just as the train passed over it, Ms. Sheinbaum said.

The Mexico City Metro has had at least two serious accidents since its inauguration half a century ago. In March of last year, a collision between two trains at the Tacubaya station left one passenger dead and injured 41 people. In 2015, a train that did not stop on time crashed into another at the Oceania station, injuring 12.

Hundreds of police officers and firefighters cordoned off the scene Tuesday as desperate friends and relatives of people believed to be on the train gathered outside the security perimeter.

Adrian Loa Martinez, 46, said that his mother called him to tell him that his half-brother and sister-in-law were driving when the overpass collapsed and that a beam fell onto their car.

He said that his sister-in-law was sent to a hospital, but that his half-brother Jose Juan Galindo was crushed and he feared he was dead. “He is down there now,” he told journalists pointing toward the site.

Gisela Rioja Castro, 43, was looking for her husband, 42-year-old Miguel Angel Espinoza. She said that her husband always takes that train after finishing work at a store, but he never arrived home and had stopped answering his phone. When she heard what happened, she immediately feared the worst but has received no information from the authorities.

“Nobody knows anything,” she said.

The collapse occurred on the newest of the Mexico City subway’s lines, Line 12, which stretches far into the city’s south side. Like many of the city’s dozen subway lines, it runs underground through more central areas of the city of 9 million, but then runs on elevated concrete structures on the city’s outskirts.

It was not clear whether a 7.1-magnitude earthquake in 2017 could have affected the subway line.