MEXICO CITY - An elevated metro line collapsed in the Mexican capital on Monday, leaving at least 23 people dead and dozens injured as a train came plunging down, authorities said.

Subway cars were seen hanging from the overpass in a tangle of twisted cables.

Mexico City Mayor Claudia Sheinbaum told reporters at the scene in the south of the capital that the dead included minors. Around 70 others were injured in the dramatic accident, one of the worst to strike the Mexico City metro since it was inaugurated in 1969.

Anxious relatives gathered at the site awaiting news of those believed to have been aboard.

Efrain Juarez said that his son was in the wreckage. "My daughter-in-law called us. She was with him and she told us the structure fell down over them," he told AFP.

The accident occurred when a section of tracks collapsed at the Olivos station at around 10 pm.

"Suddenly I saw that the structure was shaking," an unidentified witness told television network Televisa. "When the dust cleared we ran… to see if we could help. There were no screams. I don't know if they were in shock," she added.

Rescue work had to be paused because of fears the wreckage was too unstable, and Sheinbaum said a crane was on its way to continue the work. The injured were rushed to different hospitals.

One man, Jose Martinez, told reporters that he was "saved by like 15 minutes" because he was unable to leave work in time to catch the ill-fated train.

The Mexico City subway has 12 lines and carries millions of passengers each day. Line 12, where the accident struck, was inaugurated in October 2012. In October 1975, in one of the worst accidents on the network, two metro trains rammed into each other, leaving 23 dead.