"One wagon of the train fell into a river and so far seven people have been reported to have been killed," said Sukamto, a spokesman for train operator PT Kereta Api.
He said the train, which was bound for Kertapati just south-west of the south Sumatra capital Palembang, came off the rails seven kilometres (four miles) after leaving the town of Lubuklinggau.
Sukamto added the accident took place at 9:30 am (0230 GMT) but could not give more details.
Jumadi, an official of the Lubuklinggau railway station, said the accident befell the last carriage in the six-carriage train.
Aside from the dead, a total of 26 people were injured and rushed to hospitals in Lubuklinggau, Jumadi said.
The rest of the train later continued towards Kertapati, while efforts were being made to retrieve the stricken carriage, Jumadi said.
He added there were no further details about the accident yet.

Copyright AFP (Agence France-Presse), 2006