They said the bomb was allegedly planted by militants at a stone crushing factory, which exploded at around 5 am this morning when the workers came to work.
The injured were rushed to Thoubal district hospital where the condition of two was stated to be serious.
It was not known who planted the bomb, but militants who demanded money from the owner of the crusher unit seemed to be behind the crime, sources said.
The police said the area was cordoned off after the blast and search operations were launched, but no arrest was made.
No individual or group has claimed responsibility so far for the crime, they said.