The fire erupted about 2 a.m. as the train was traveling from Mumbai in western India to Dehradun in the northern state of Uttarakhand.
The blaze began in one of the sleeper coaches as the passengers slept and spread to two more when the train was about 90 miles north of Mumbai, NDTV reported.
The Times of India said the train was near the Dahanu railway station in Maharashtra state at the time of the fire.
The Hindustan Times said the fire was noticed by an attendant at a railroad crossing, who later informed the engineer and the train was stopped. Rescuers were then able to evacuate other passengers to safety.
Railroad authorities said the victims were asphyxiated, CNN-IBN said.
Although the cause of fire remained under investigation, the report quoted sources as saying burned cables were found under an electricity panel in one of the coaches, suggesting a short circuit.
"The casualties are unlikely to rise because all checks have been done," a senior railway ministry spokesman said. "We don't know the cause of the fire as yet."
Those killed included a woman and four men. The rest were yet to be identified, CNN-IBN reported.
In a similar disaster late last month in south India, a fire in a sleeper coach of a train killed at least 26 people and injured eight.