Mexico City, Mexico - At least 20 people, including children, were killed after a subway bridge partially collapsed in Mexico City on Monday evening.

Another 34 people were taken to hospital, Mayor Claudia Sheinbaum told reporters.

Several carriages of a line 12 subway train plunged dozens of feet deep and collided with each other, videos circulating on social media showed.

Initial findings showed part of the bridge gave way, Sheinbaum said.

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Footage also showed rescuers using a ladder to pull passengers out of train cars as they were hanging.

Cars had been travelling underneath the collapsed section of the overpass at Olivos station on the south-eastern edge of the city.

Because of the train's unstable position, rescue efforts had to be suspended, Sheinbaum said.

Authorities said at least 70 people had been injured in total.