A 20-year-old sheriff's deputy who shot dead six people in the US state of Wisconsin has been killed following a police manhunt.

The Forest County Sheriff's Department in Crandon said seven people were dead, including the 20-year-old gunman Tyler Peterson.

Crandon, a town of about 2,000 people, is about 290km north of Milwaukee.

Five of the victims ranged in age from 14 to 20. The age of a sixth was not released.

Another victim is reported to be in a critical condition.

Mr Peterson, who was said to have stormed into his ex-girlfriend's house, was later shot dead, although authorities have not confirmed who shot him. His former girlfriend was among those who died.

Authorities responded to reports of shots fired at about 3am local time yesterday (8am Irish time).

The investigation was being handled by the state Department of Criminal Investigation because a local law enforcement officer was involved.

Mr Peterson was a Forest County sheriff's deputy and part-time police officer in Crandon.

Local authorities released little information on the killings.