Gun-toting home intruders left a man lying on his lawn with a fractured neck in an attack that traumatised the victim and his partner and child, police say.

Invercargill Police are investigating the incident, which happened about 11pm on Monday at an address on Limestone Plains Road, Thornbury, Detective Sergeant John Kean said.

The family woke to the sound of knocking, and when they opened the door they were confronted with a person holding a gun, Kean said.

Three people forced their way into the house. It is believed at least two of them were carrying firearms.

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"A struggle then ensued," Kean said. "The male occupant was taken outside, assaulted and was left lying injured on the lawn."

The offenders left the property in a car and are thought to have travelled towards the Thornbury township.

"It is believed possible that a fourth person was involved who was driving the vehicle.

"The offenders, prior to leaving, have attempted to search the house although at this point it is not known if anything has been stolen.

"The male victim received fractures to his neck along with a laceration to his head and was treated at Southland Hospital and has been discharged.

"Both he and his partner along with their child who was also home at the time have been traumatised by this serious, cowardly and unprovoked attack."

Police today conducted a scene examination. There are currently 10 officers working on the investigation.

Police want to hear from anyone who may have information on the attack. Call the Invercargill Police station on (03) 211 0500 or phone Crimestoppers anonymously on 0800 555 111.