told reporters early Tuesday. “There has to be a deep investigation, and whoever is responsible has to be held responsible.”
In the meantime, she said, Line 12 would remain closed as the authorities investigate the cause of the accident. Mexico City Metro advised people to avoid the area.
Ms. Sheinbaum did not rule out the possibility of further incidents on the damaged train line, and said that the avenue that runs below the line would be shut down during an investigation.
Marcelo Ebrard, Mexico’s foreign minister, called the crash a “terrible tragedy” in a Twitter post late Monday. “Of course, the causes should be investigated and the responsibilities for it defined.”
Mr. Ebard was mayor of Mexico City from 2006 to 2012, when the new line was constructed, and accusations of poor construction and planning emerged almost as soon as it was opened. The line was closed briefly in 2013 for repairs.
Hundreds of police officers and firefighters cordoned off the scene on Tuesday morning as relatives and friends of people believed to have been on the train gathered outside the security perimeter to seek information.
Mayor Sheinbaum said that at least one person trapped in a car in the mountain of rubble had been pulled out alive and taken to the hospital.