MUMBAI, India -?A deadly fire engulfed three cars of a passenger train early Wednesday, killing nine people as they slept in the latest tragedy to hit India's vast railway network, officials said.

Authorities are trying to determine what caused the fire to break out before dawn, just hours after the train left Mumbai on a 48-hour journey to the Himalayan foothill town of Dehradun, Western Railways spokesman Sunil Singh said. ?

The fire spread through three of the train's coaches before it was noticed by a guard at a railway post, who alerted authorities. The train was then stopped and the blaze extinguished, officials said.

TV channels broadcast images of the charred and blackened cars, which were unhooked from the rest of the train so it could continue its journey north.

Police said four people were injured in the blaze, which happened less than two weeks after another train fire killed 26 people in the southern state of Andhra Pradesh.

Accidents are common on India's railroad network, one of the world's largest, with 23 million passengers daily riding on about 11,000 passenger trains. Most collisions and fires are blamed on poor maintenance and human error.

Fires were involved in at least eight of the 100 or so accidents that killed 185 people in 2012, according to a 2013 safety review submitted to parliament.

The railway ministry on Wednesday promised about $8,000 in compensation to the families of those killed aboard the Mumbai-Dehradun Express.