A person armed with a handgun was reported at the South Auckland home where police later found the bodies of a man and a woman, police say.

Police were speaking with a 30-year-old male - who was in their custody - in relation to the double homicide, but said he was in custody for an unrelated offence.

Emergency services were called to a home in Gambare Place Wattle Downs at 1.45pm on Thursday following a report of person armed with a handgun at the property and a woman injured, Detective Inspector Tofilau Faamanuia Va'aelua said.

The woman was found dead when police arrived, Faamanuia Va'aelua said, and a man was found dead shortly after on the same property.

Both had fatal gunshot wounds, Faamanuia Va'aelua said.

A forensic scene examination was underway on Friday at the scene.

"I can confirm we are speaking with a 30-year-old man who is currently in custody for an unrelated offence. We are working to determine whether this man is involved.

"That determination relies on the outcome of our enquiries, which we're prioritising with urgency," Faamanuia Va'aelua said.

"We are maintaining an open mind, hence why no charges have been laid at this stage.

"Alongside this, post-mortems for the two victims are underway today."

Police were asking anyone had any information that could help police to come forward.

"We know this will be an unsettling time for those in our community, that such a violent incident has taken place.

"I want to reassure people we are working hard to hold people to account.

An increased police presence would remain in the area, he said.

Information could be reported online at 105.police.govt.nz, and clicking "Update Report", or by calling 105, using the reference number 260827/1324 and quote Operation Bealey.

Anonymous reports could also be made through Crime Stoppers, by calling 0800 555 111.