“Civil police ... are investigating what kind of bomb it was and why anyone could have placed the bomb.” Security has been tightened across India as the country holds a six-week general election which has been marred by deadly violence in other parts of the country, including attacks by Maoist rebels.
Voting has already taken place in most major cities, including Chennai which went to the polls last week
Sources say a man has been held and is being questioned. He was reportedly hiding inside the train an hour after the explosions.
A National Investigation Agency team is going to Chennai to join the investigations.