LORIENT, France (AFP) - A French policeman has been left clinically dead after being stabbed through the eye by a psychiatric patient who had been released into the community, a public prosecutor said on Friday.

Lorient prosecutor Alexis Bouroz told AFP the officer, a 49-year-old married father of two, was in a "state of clinical death", after being attacked while responding to a call to investigate loud screaming at a house in the town in Britanny, western France.

As soon as the officer knocked on the door, the 35-year-old resident charged out naked and plunged a knife through his eye and deep into his skull.

One of the two other policemen with the victim was slightly injured while a third officer was able to overcome the assailant.

The perpetrator of the attack was described as having a long history of psychiatric disorders and had been incarcerated in a clinic near Paris for 18 months up to July 2011.

In Lorient he was being treated as an outpatient.