Mohammed Imam Ul Haq has been struggling to find his missing brother and to claim his nephew's body from the many corpses lying in city hospitals following India's worst train accident in two decades on Friday.

Haq's brother and two nephews were on the Coromandel Express, one of the three trains that crashed into each other in the Balasore district of the eastern state of Odisha. The incident left 275 people dead and more than 1,200 injured.

For Haq, from the eastern state of Bihar, the tragedy is two-fold. As his brother remains missing, a body he says is that of his 12-year-old nephew is also being claimed by another family.

"We are left with no option but to do a DNA test to determine whose body it is. The whole process takes really long. I hope we can claim the body soon," a distraught Haq told Reuters at the All India Institute of Medical Sciences (AIIMS) in Odisha's capital of Bhubaneswar.

Nearly a hundred bodies remained unclaimed in several hospitals and mortuaries across Odisha as of late Monday, officials said.

Authorities had taken DNA samples from all the dead bodies in hospitals across the state, senior police official Prateek Singh told reporters on Tuesday.

"In cases where there are multiple claimants, we have taken DNA samples from family members and we will preserve the bodies until the DNA matches," Singh told local media.

The trains had passengers from several states and officials from seven states - Assam, Bihar, Jharkhand, West Bengal, Tamil Nadu, Karnataka and Andhra Pradesh - were in Balasore to help people claim the bodies of family members and take them home, Singh said.

Desperate families scoured hospitals and mortuaries in search of their loved ones, but the gruesome condition of the corpses made identification a challenge.

"We are Muslim, boys are circumcised at birth; however, the body is in no condition to even check that," Haq said of the remains he believes are of his nephew.