The cause of India's deadliest train disaster in decades was linked to the signal system, the railway minister has said, as families scoured hospitals and morgues for missing relatives with the death toll revised to 275.
Mounds of debris were piled high at the site of Friday night's crash near Balasore in the eastern state of Odisha, as workers started to clear the smashed carriages and the blood-stained wreckage where hundreds were also wounded.
Hospitals have been overwhelmed by the number of casualties.
"We have identified the cause of the accident and the people responsible for it," India's Railway Minister Ashwini Vaishnaw told news agency ANI.
However, he said it was "not appropriate" to give details before a final investigation report.
There was confusion about the exact sequence of events, but reports cited railway officials saying a signalling error had sent the Coromandal Express running south from Kolkata to Chennai onto a side track.
It slammed into a freight train and the wreckage derailed an express running north from India's tech hub Bengaluru to Kolkata that was also passing the site.
Odisha state's chief secretary Pradeep Jena confirmed that about 900 injured people had been hospitalised.
Mr Vaishnaw said the "change that occurred during electronic interlocking, the accident happened due to that", a technical term referring to a complex signal system designed to stop trains colliding by arranging their movement on the tracks.
"Whoever did it, and how it happened, will be found out after proper investigation," he added.
Prime Minister Narendra Modi visited the crash site and injured passengers being treated in hospital yesterday and said "no one responsible" would be spared.
"I pray that we get out of this sad moment as soon as possible," he told state broadcaster Doordarshan.
The rescue effort was declared over yesterday evening after emergency personnel had searched the mangled wreckage for survivors and laid scores of bodies out under white sheets beside the tracks.
A school close to the crash site had been turned into a makeshift morgue, but officials said many of the bodies were so disfigured that several distraught families could only spot their loved ones by pieces of jewellery.
In sweltering heat, many of the bodies were being transferred to bigger centres and officials suggested some would only be identified by DNA testing.
Mohammad Abid, 35, said his 18-year-old son had somehow survived the crash without injuries, but he was looking for his cousin, who had been travelling with him.
"I want to know how two trains were allowed on the same track ... someone should be punished for this," Abid said.
Relatives searching for loved ones
Grief-stricken Vishwanath Sahni, 47, was searching for his 26-year-old son Manoj Kumar, who had been travelling to Chennai for work in the textile industry.
After touring every hospital that he could, he was now waiting at a morgue.
"I don't know if I'll find my son and how they'll be able to ensure that I only get my son's body, if he's here," he said.
Beside him waited his friend Mahender Yadav, 60, whose two sons travelling with Kumar were recovering in hospital.
"One of them has serious injuries, but I know that they are in a hospital and doctors will do their best," Yadav said. "I just wanted to be with Sahni and hope that he finds his son."
Authorities said every hospital between the crash site and the state capital Bhubaneswar, around 200km away, had received victims. Around 200 ambulances, and even buses, were deployed to transport them.
India has one of the world's largest rail networks and has seen several disasters over the years.
The worst of them was in 1981 when a train derailed while crossing a bridge in Bihar and plunged into the river below, killing between 800 and 1,000 people.
Friday's crash ranks as its third-worst, and the deadliest since 1995, when two express trains collided in Firozabad, near Agra, killing more than 300 people.
The disaster comes despite new investments and upgrades in technology that have significantly improved railway safety in recent years.
Condolences have poured in from around the world, including from Pope Francis, the UN Secretary-General Antonio Guterres, US Secretary of State Antony Blinken and French President Emmanuel Macron.