Death toll from Mexico City overpass collapse tops 20

Questions and accusations swirl around the dangerous scene - NBC's Laura Aguirre reports

MEXICO CITY, Mexico (KYMA, KECY/NBC News) - A second in time - a life-changing disaster. A commuter train overpass gave way 16-feet above a busy Mexico City street Monday night, crushing passing vehicles below.

Chaos in the aftermath; rescue crews rushing in to find survivors and help the injured, families racing to the scene, pictures on cell phones shown to rescuers, desperate for any word on loved ones.

This woman frantically looking for her sister who rides the train home. Another woman received a call from her husband's cell phone, the call from a stranger who found the phone on the ground. Still no word on her husband, or his condition.

Rescue and recovery efforts continue slowly amid the shifting unstable debris.

Mexico's foreign relations minister calls the collapse the most terrible accident in the country's mass transportation system. It happened on one of the city's newest train lines. The city's mayor, and other leaders, vow a full investigation will take place. But for many families, the concern over the city's railway system is coming too late.