MEXICO CITY -- The death toll from the collapse of an overpass on the Mexico City metro line rose to 24 Tuesday as crews untangled train carriages from the steel and concrete wreckage that fell onto a roadway.
Monday night's accident was one of the deadliest in the history of the subway, and questions quickly arose about the structural integrity of the mass transit system, among the world's busiest.
Another 27 people remained hospitalized of the more than 70 injured when the support beams collapsed about 10:30 p.m. as a train passed along the elevated section, said Mayor Claudia Sheinbaum.
On Tuesday, a crane carefully lowered a train car containing four bodies to the ground.
Of the 24 people killed, 21 died at the scene, while the others died at hospitals. Only five have been identified so far. Children were among the fatalities, Sheinbaum said.
Initial analysis pointed to a "presumed structural failure," Sheinbaum said, promising a thorough and independent inquiry. She added that a Norwegian firm had been hired to investigate.
"I did not have any report nor alert of any problem that could have led us to this situation," she said.
The overpass was about 16 feet above the road in the borough of Tlahuac, but the train ran above a concrete median strip, which apparently lessened the casualties among motorists.
The Mexico City Metro -- which is among the world's cheapest with tickets costing about 25 cents -- has had at least three serious accidents since its inauguration half a century ago. In March 2020, a collision between two trains at the Tacubaya station left one passenger dead and injured 41. In 2015, a train that did not stop on time crashed into another at the Oceania station, injuring 12. In October 1975, at least 26 people were killed in another accident.
A magnitude-7.1 earthquake in 2017 exposed dangerous construction defects in the elevated line near where Monday's accident occurred. Authorities at the time had done patchwork repairs on the columns and horizontal beams.
The collapse occurred on Line 12, the subway's newest, that stretches to the city's south side. Like many of the dozen subway lines, it runs underground through more central areas of the city of 9 million but is on elevated concrete structures on the outskirts.
A report issued by the subway system including photos in 2017 showed that the base of one vertical column supporting the tracks had cracked and shed layers of concrete because not enough steel rebar stirrups had been used when it was built around 2010. In 2017, authorities patched and widened the column by injecting resins, wrapping it in carbon fiber, building a jacket of additional rebar around the base and pouring concrete around the collar.
Authorities also found that one of the horizontal beams had come loose from its support at the top of a vertical column and was sagging -- the kind of failure that could have contributed to Monday's collapse. Authorities at the time welded steel diagonal braces to the bottom of the beam, chipped out and repoured fractured concrete elements.
Mexican foreign affairs secretary Marcelo Ebrard called the collapse "the most terrible accident we have ever had in mass transportation." Ebrard was Mexico City's mayor from 2006 to 2012, when the affected line was built.
Allegations of poor design and construction on the subway line emerged soon after the Ebrard left office as mayor. The line had to be partly closed in 2013 so tracks could be repaired.
Ebrard, who leads Mexico's efforts to obtain coronavirus vaccines, has been considered a potential presidential candidate in 2024.
"Of course, the causes should be investigated and those responsible should be identified," he wrote. "I repeat that I am entirely at the disposition of authorities to contribute in whatever way is necessary."
On Monday night, hundreds of police officers and firefighters cordoned off the scene as desperate friends and relatives of people believed to be on the train gathered. Despite the fact that the coronavirus situation remains serious in Mexico City, they crowded together waiting for news.
Adrian Loa Martinez, 46, said his mother called him to tell him that his half brother and sister-in-law were driving when the overpass collapsed and that a beam fell onto their car.
He said that his sister-in-law was sent to a hospital, but that his half brother Jose Juan Galindo was crushed and he feared he was dead. "He is down there now," he told journalists, pointing to the site.
The line was closed Tuesday and hundreds of buses were called in. Thousands in surrounding neighborhoods lined up before dawn to catch the buses for work.
Information for this article was contributed by E. Eduardo Castillo, Mark Stevenson and MarIa Verza of The Associated Press.