At least 45 people were killed and scores badly injured on Monday in southern Pakistan, after an express train crashed into the derailed carriages of another passenger train. Rescuers worked through the day to reach survivors, using heavy machinery to lift the mangled carriages. The crash took place at around 3.30am in Ghotki district when most of the 1,200 passengers on the two trains were sleeping. It was the latest train accident in the nation of more than 220 million people. Prime Minister Imran Khan ordered an immediate investigation into the crash, while his political opponents were quick to attack his failure to improve the safety of the overworked railway network. Railway officials said carriages of the Millat Express had derailed near Daharki and fallen on the adjacent track as the service made its way north from the port city of Karachi. The oncoming Sir Syed Express from Rawalpindi to Karachi then hit the wreckage. Four railway employees were reported to be among the dead. "We tumbled upon each other, but that was not fatal," Akhtar Rajput, a passenger on the train that derailed, told AFP. "Then another train hit us from nowhere, and that hit us harder. When I regained my senses, I saw passengers lying around me, some were trying to get out of the coach." A local official said 13 to 14 carriages had derailed and six were “completely destroyed". The driver of the Sir Syed Express told Geo News he had desperately tried to apply the emergency brake when he saw the derailed coaches, but failed to stop the train. Usman Abdullah, Ghotki's deputy commissioner, told Geo News: “This is a challenging task. It will take time to use heavy machinery to free citizens [still trapped]." Mr Abdullah said the death toll steadily rose through the day, reaching at least 45. Lighting was being brought in so the rescue work could continue through the night if needed, although the chances of finding survivors were diminishing, he said. Pakistan's trains have suffered from decades of underinvestment under successive governments and the accident was at least the fifth deadly rail incident since Mr Khan took office three years ago. The former cricketer said he was “shocked by the horrific train accident at Ghotki early this morning” and was ordering a “comprehensive investigation into railway safety faultlines”. Senator Sherry Rehman, an opposition leader with the Pakistan Peoples Party, called for the resignation of the railways minister. She said: “My heart goes out to the families of the deceased and grievously hurt. In other countries, the minister would resign, especially after so many train wrecks in the last three years.” Shehbaz Sharif, leader of the opposition in the national assembly, said the railways were “in an utter shambles today in terms of safety and finances”. In February 2020, at least 19 people were killed when a train collided with a passenger bus near Sindh’s Rohri. Three months earlier, more than 70 had died in a fire aboard a moving train after carriages caught alight near Rahim Yar Khan in Punjab. Troops joined the rescue efforts on Monday morning, according to a statement from the military's information wing. Military doctors, as well as paramedics and engineers, were at the site, and a specialist search team was being flown by helicopter from Rawalpindi. Chinese investment as part of Beijing's Belt and Road initiative to build a modern-day Silk Road would have upgraded Pakistan's trains, but the plans have been delayed in a disagreement over financing.