Seven explosions rocked Mumbai’s commuter rail network during the evening’s rush hour, a railway spokesman said.
The blasts ripped apart train compartments and reportedly killed dozens, police and Indian media said.
There was chaos throughout Mumbai’s crowded rail network following the explosions, and authorities struggled to determine how many people had been killed and injured.
But Indian television reports indicated the death toll could be in the dozens.
Television images showed injured victims sprawled on train tracks, frantically dialling their mobile phones.
Some of the injured were being carried away from the crash site.
The force of the blasts ripped doors and windows off carriages, and luggage and debris were strewn about.
Pranay Prabhakar, the spokesman for the Western Railway, confirmed seven blasts had taken place.
He said all trains had been suspended, and he appealed to the public to stay away from the city’s train stations.
Mumbai, India’s financial centre, and New Delhi, the capital, were reportedly on high alert.
Mumbai’s commuter rail network is among the most crowded in the world.