The death toll from the collapse of an overpass on the Mexico City metro has climbed to 24, as crews worked to clear the wreckage – and anger grew over the latest in a string of catastrophes to hit one of the world’s largest mass transit systems. Officials refused to speculate on the cause of the Monday night disaster which sent two carriages crashing into passing traffic on the street below. The city’s mayor, Claudia Sheinbaum, promised a thorough investigation by an outside firm and the federal prosecutor’s office – though she stood by the embattled director of the metro, Florencia Serranía. “We’re going to get to the truth. We’re not going to cover anything up. This is the request we’re making to the prosecutor’s office. There will be accountability,” she said at a tense press conference on Tuesday. President Andrés Manuel López Obrador called for a swift and open investigation. “There’s no impunity for anyone,” he told reporters. Mexico’s capital has been governed since 2000 by former mayor López Obrador and his allies. Footage from security cameras showed the overpass collapsing on to a busy street about 10.30pm on Monday night, leaving one of the wagons dangling precariously. “We only heard a thunderous noise and everything started coming apart,” a survivor identifying herself as Mariana told the newspaper El Universal. “We were sent flying and hit the ceiling.” Bystanders and passersby rushed to pull survivors from the wreck. Adolfo Ángel Ibarra, 21, was travelling on a small bus when he heard the roar of collapsing concrete and turned around to see a cloud of dust. Running to the scene he and other bystanders forced open the door and pulled stunned survivors from the wreckage. “I was scared, but I also felt like a hero. I felt like someone who was needed,” Ibarra said from the scene near the Los Olivos metro station. Emergency medical crews and firefighters worked through the night to free trapped passengers, and 79 people were taken to hospital. Families of missing passengers joined in the desperate search at the scene and pleaded for information at overwhelmed hospitals. One mother identified as Marisol Tapía interrupted a press conference held on Tuesday morning by an opposition party at the scene of the crash to demand answers. “We’ve searched all night and nobody knows where he is,” Tapía wailed as she pressed for an answer on the whereabouts of her son Giovani Hernández Tapía, 13. Serranía said the collapsed metro line – which was inaugurated in 2012 – was last inspected in January 2020. The collapse followed a spate of calamities in the metro, including trains crashing into each other and a fire tearing through the system’s central command centre. It also occurred on Line 12 – the “Golden Line” – which opened to fanfare as a modernization of Mexico City’s metro, but was beset by closures and construction problems. Mexican social media resurfaced old tweets and posts from people warning something was amiss with the elevated metro line. “I always said one day it’s going to collapse,” said Paulina García, 45, a resident of the crash area in the south-eastern Tláhuac borough. “There have been problems since it was inaugurated,” she said, as nearby a crane lifted one of the fallen wagons so it could be hauled away. Homero Zavala, leader of the metro workers’ union, said four of the lines were “time bombs” due to dilapidated infrastructure. “This accident … could have been avoided if they listened to workers,” he told reporters. Line 12 carried approximately 350,000 passengers daily from the semi-rural south-eastern borough of Tláhuac to a south-central part of the capital. Its inauguration was heralded as a long-overdue infrastructure advancement for a metro system founded in 1969, but chronically underfunded and rife with dilapidated infrastructure. Line 12 was supposed to be the crowning achievement of former mayor Marcelo Ebrard, who left office in 2012 and is now foreign minister – and a close ally of the president. Political observers consider Ebrard and Sheinbaum to be rivals in the succession to López Obrador, who steps down in 2024.