“A support beam gave way,” Sheinbaum said, adding that the beam collapsed just as the train passed over it.
Sheinbaum said 15 people were killed and that a car was trapped under the rubble.
Rescue efforts were briefly interrupted at midnight because the partially hanging train was “very weak” and a crane had to be brought in. There were still people trapped inside the train, though “we don’t know if they are alive,” said Sheinbaum.
The city’s Comprehensive Risk Management and Civil Protection Agency initially put the toll at 13 and 70 people injured.
The metro’s 12 line was built when Foreign Minister Marcelo Ebrard was mayor of Mexico City. The construction of the line has been plagued by complaints and accusations of irregularities.
“What happened today with the Metro is a terrible tragedy. My solidarity with the victims and their families,” Ebrard said on Twitter.