The father of a man shot dead by police says he believes his son was unarmed when officers fired at him.

Steve Protheroe's 36-year-old son was shot by a detective outside a Brisbane home just before noon on Tuesday.

Police say the man threatened officers with a gun at the Bracken Ridge house.

Mr Protheroe says he'd told detectives where to find his son but didn't imagine his boy would be killed.

He didn't believe "for half a second" that his son had had a gun, he told the Nine Network.

"I believe it's nothing but a made-up, trumped-up load of nonsense," he said.

"I believe the police went there, I believe that they put him in a corner and I believe they shot him.

"I don't believe there was any weapon whatsoever."

Mr Protheroe said when he'd told detectives where to find his son, he'd told them he wasn't violent.

"I told them he'd probably run, if anything else he'd run, but that's it," he said.

"Two hours later I get a phone call to say my son is dead (from) my (other) son.

"The police did not even bother to tell me anything."

Police Union president Ian Leavers earlier told reporters outside the cordoned-off Ivor Street house he'd spoken with the detective involved in the shooting.

Mr Leavers said two officers had gone to the house to investigate property offences, and the man's girlfriend had allowed them to search the house.

As they were leaving from the rear of the home the detectives confronted a man outside, and the man then drew a semi-automatic pistol.

One officer ran around the side of the house, while the other ran into a garage, and the gunman followed him inside.

"When confronted with the firearm and cornered, this officer had no option but to defend himself," Mr Leavers told reporters at the scene.

"This officer has actually been hunted by this man."

Mr Leavers said there was no time for negotiation.

"It was either shoot or be shot," he said.

Mr Leavers said the 36-year-old gunman was shot in the chest and stomach.

"Police produced their firearms and fired a volley of shots, and two shots hit the man," he said, adding the man was well known to police.

The Department of Community Safety confirmed that paramedics had been called to the house just before noon and they performed CPR on a patient who was in a critical condition.

The man died 45 minutes later, according to Mr Leavers.

Two young children were inside the house at the time of the shooting, he added.

A neighbour told AAP he heard gunshots followed by a woman shouting.

"I was sitting inside when I heard three quick consecutive shots," said the elderly man, who did not want to be identified.

"I heard a woman shout out, 'They shot him.'"

The neighbour said he saw ambulances and a woman being taken away in the back of a police vehicle.

"She looked very distressed," he said.

Another neighbour said she'd often seen police at the address.

"It has been a noisy household, that one. There's always fighting going on," Carol Biviano told AAP.

"I have seen cops show up there many times."

Acting Detective Superintendent Bob Hytch said the two plain-clothes officers were assisting the police service's ethical standards command unit.