At least 80 people were killed and 850 injured after two passenger trains collided in the eastern Indian state of Odisha on Friday, state Chief Secretary Pradeep Jena said.
The Coromandel Express, which runs from Kolkata to Chennai, collided with another passenger train, the Howrah Superfast Express, railway officials said on Friday evening.
Images from the scene showed rescuers climbing up the mangled wreck of one of the trains to find survivors.
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 bloods, broken limbs and people dying around me," an eyewitness told Reuters.
The Howrah Superfast Express derailed and became entangled with the Coromandel Express, South Eastern Railway authorities said in a statement.
Jena said earlier that hundreds of people were taken to different local hospitals near the accident site, adding that more than 200 ambulances had been rushed to take accident victims to nearby hospitals.
Odisha Chief Minister Naveen Patnaik said authorities' priority was "removing the living to the hospitals, that's our first concern, to look after the living".
Rescue operations were underway at the site and "all possible assistance" is being given to those affected, Prime Minister Narendra Modi said in a tweet.
Rescue teams have been mobilised from Odisha's Bhubaneswar and Kolkata in West Bengal, federal Minister for Railways Ashwini Vaishnaw said in a tweet.
The National Disaster Response Force, state government teams and the air force had also mobilised to respond to the incident, he added.
People try to escape from toppled compartments, following the deadly collision of two trains, in Balasore in this screen grab obtained from a video. ANI/Reuters TV via REUTERS.
A view of a damaged compartment, following the deadly collision of two trains, in Balasore, India in this screen grab obtained from a video. ANI/Reuters TV via REUTERS.
A view of a damaged compartment, following the deadly collision of two trains, in Balasore, India in this screen grab obtained from a video. ANI/Reuters TV via REUTERS.