The bomb was hurled at the camp of non-Manipuri labourers by suspected militants, the sources said.
Earlier, the police had said that the bomb was planted in a shop and exploded.
All the eight persons who died on the spot were non-Manipuri persons, sources said adding the injured were also non-Manipuri.
The bomb was so powerful that the blast was heard one kilometre away from the spot.
No individual or group has claimed responsibility for the blast, the sources added.