The incident happened at about 1.20pm this afternoon at a house in Lea Gate.
Police said they were called to the scene by the North West Ambulance Service, who were responding to a report that a man had suffered "a serious hand injury".
The man, who is believed to be in his mid 20s, has been taken to hospital, but his injuries are not said to be life-threatening.
Det Ch Insp Sarah Jackson said: “The man has suffered an extremely serious injury to his hand and our investigation into this incident is very much in its infancy.
“It would not be helpful or appropriate to speculate on what has gone on until the full facts are known but I want to reassure residents’ living nearby that this is an isolated incident and there is nothing to suggest any threat to the wider community.”
Police said the circumstances of the incident are still being investigated.
Lea Gate was closed between Turton Road and Morrisons in Harwood, but has now reopened.