Man shot by WA Police 'held fake gun'

A man who was shot by police in his Perth home had threateningly brandished a replica gun after inviting them there alleging someone was trespassing.

Acting assistant commissioner for the metropolitan region Greg Knott said the man called police to his Waikiki property on Sunday afternoon and swiftly confronted the two attending officers with the fake gun.

The officers both drew their firearms, and one of them fired more than one shot.

"In such circumstances they need to make split-second decisions about the threat they are facing, what their options are and what their final course of action is going to be," Mr Knott told reporters.

"These incidents are very traumatic for the officers, just as much they are for the person involved."

The man sustained a non life-threatening wound to his arm and is under police guard in Royal Perth Hospital, where he had surgery on Monday.

He has not yet been interviewed by police or charged, and is being detained under the Mental Health Act.

The incident, which is estimated to have lasted 40 seconds, is being investigated by the Internal Affairs Unit.