At least 20 people were killed—including children—when a subway overpass collapsed in Mexico City late Monday, sending several train cars plummeting down onto traffic below. Mayor Claudia Sheinbaum said 70 people were hurt but survived the catastrophe, although seven of them have been left in a serious condition. Horrific security footage showed the collapse on the metro’s Line 12, which is suspended about five meters above the busy roadway. “There are unfortunately children among the dead,” Sheinbaum said, adding that a support beam appeared to have failed to cause the collapse. Mexico’s Foreign Relations Secretary Marcelo Ebrard was Mexico City mayor when Line 12 was built. According to the Associated Press, he wrote in an early Tuesday statement: “What happened today on the metro is a terrible tragedy... I am entirely at the disposition of authorities to contribute in whatever way is necessary.”