At least 207 people were killed and 900 injured when two passenger trains collided in Odisha, according to government officials in the eastern Indian state, in India's deadliest rail accident in over a decade.
The death toll is expected to increase, state Chief Secretary Pradeep Jena said in a tweet.
Sudhanshu Sarangi, the director general of the fire department in Odisha, said that 207 bodies had been recovered so far.
Images from the scene showed rescuers climbing up the wreck of one of the trains to find survivors.
Videos shared on social media showed the arrival of several ambulances and people being pulled out of the upturned train coaches.
Rescue teams have been mobilised from Odisha's Bhubaneswar and Kolkata in West Bengal, federal Minister for Railways Ashwini Vaishnaw said in a tweet late this evening.
Three National Disaster Response Force teams are at the site of the accident, and six more teams are being mobilised, the country's National Disaster Response Force said.
The collision occurred at about 7pm local time (2:30pm Irish time) when the Howrah Superfast Express, running from Bangalore to Howrah, West Bengal, derailed and became entangled with the Coromandel Express, which runs from Kolkata to Chennai, railway officials said.
'All possible assistance'
Odisha Chief Minister Naveen Patnaik said authorities' priority was "removing the living to the hospitals".
Rescue operations were underway at the site and "all possible assistance" was being given to those affected, Prime Minister Narendra Modi said in a tweet.
Images broadcast on local stations showed smashed train compartments torn open with blood-stained holes of twisted metal, and scores of passengers lying beside the tracks near Balasore, about 200 kilometres from the state capital Bhubaneswar.
"Our top priority now is rescuing (the passengers) and providing health support to the injured," Mr Jena said earlier.
Amitabh Sharma, executive director with the Indian Railways, told AFP that the two passenger trains "had an active involvement in the accident" while "the third train, a goods train, which was parked at the site, also got (involved) in the accident".
With rescuers at the crash site pulling the wounded out of the wreckage, fears mounted that the toll could still rise higher, but officials could not give exact figures.
"The casualty figures from the ground or clarity on the number of injured is very difficult to assess for us at this moment," Mr Sharma said, amid reports that many passengers were still believed to be trapped under mangled rail cars.
Anil Kumar Mohanty, a medical officer in Balasore, told AFP that "we have rushed doctors and medical staff to the accident site".
Hundreds of young people lined up outside a government hospital in Odisha's Soro to donate blood.
"I was there at the site and I can see blood, broken limbs and people dying around me," an eyewitness told Reuters.
One survivor told local TV news reporters that he had been sleeping when the accident happened, and woke to find himself trapped under around a dozen fellow passengers, before somehow crawling out from the carriage with only injuries to his neck and arm.
Another TV station showed graphic images of a train car toppled to one side of the track, as local residents tried to pull victims to safety.
'All hands required'
SK Panda, a spokesperson in Jena's office in Odisha state, called it "a heavy accident".
"We expect that the rescue work will continue till at least tomorrow morning," Mr Panda said. "On our part, we have prepared all big government and private hospitals from the accident site to the state capital to cater to the injured."
The spokesperson added that authorities had already rushed "75 ambulances to the site and had also deployed many buses" to transport both the injured passengers and survivors from the site.
Indian Prime Minister Narendra Modi said he was "distressed by the train accident".
"In this hour of grief, my thoughts are with the bereaved families. May the injured recover soon", Modi said on Twitter, adding that he had spoken to railways minister Ashwini Vaishnaw to take "stock of the situation".
Mr Vaishnaw said that he was rushing to the accident site.
India is no stranger to railway accidents and has seen several such incidents in the past, but railway safety - thanks to massive new investments and upgrades in technology - has improved significantly in recent years.
