The derailment occurred around 4 a.M. About 70 kms from Delhi, Alok Mittal, the IGP of the Rohtak Range, said.
Six bogies of the second-class sleeper (S-5 to S-10), one luggage compartment and the guard coach were derailed, railway officials said, adding five of the coaches overturned.
Railway authorities have ordered a probe into the accident.
They said that at least 50 metres of the rail track was found broken at the accident site.
"We are trying to ascertain whether the railway track broke due to the accident or whether the broken track led to the accident," a railway official at the accident site said.
"Most of the passengers in the derailed coaches were sleeping when the accident took place," said police officials.
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26 injured were admitted to the Postgraduate Institute of Medical Sciences (PGIMS) at Rohtak, officials said, adding one patient has suffered head injuries.
The others do not have any major injuries.
Traffic on the Rohtak-Delhi section was affected. Efforts were on to clear the track. 30 trains, including 16 local ones, were affected. They were either cancelled, diverted or short terminated.
"Someone onboard the train had made a call to police control room. We promptly reached the spot and helped railway officials in rescue operation," said Mittal.
"The Railways Minister himself spoke to the locomotive driver as well as hospital authorities in the morning. He also spoke to the Divisional Railway Manager. The Railways will bear the cost of treatment," officials said.