The union said it was "patently untrue" Jai Hunt was not wielding a knife when shot in the upper body at his home in suburban Springfield, southwest of Brisbane, on Wednesday afternoon.

Going on information from initial investigations, commissioner Ian Stewart also supported the actions of officers, despite family friend Michelle Wykes saying Jai had been disarmed by his father before being shot.

"I will back those officers on what I've been told so far," Mr Stewart said on Thursday afternoon.

"They made good choices, good decisions to protect not only themselves but other (people) who were present."

Police allege Jai lunged at two officers with a knife but Ms Wykes said he hadn't even threatened them.

"Jai was unarmed when the police officer actually shot him," she said on Thursday.

Queensland Police Union president Ian Leavers dismissed her statement and was standing by the officers.

"It's not the first time we've had families come out and say things which are just patently untrue," Mr Leavers said.

"If someone comes at you with a knife and you're in fear of grievous bodily harm or death, you are authorised and justified to use your firearm to defend yourself or the life of somebody else."

The officers involved had no choice but to open fire, Mr Leavers said.

"It is not the case where police were having a discussion and trying to mediate things, this happened as they arrived," he said.

"At the end of the day, they go to work and they will go home at the end of their shift and they will use their firearm to protect their lives and the lives of others."

The officers who shot Jai were wearing body cameras and captured footage will be reviewed under an internal police investigation.

"They are trained, particularly where a bladed weapon is involved, to consider all their uses of force and the entire circumstances," Mr Stewart said.

"This happened very quickly."

Meanwhile, Jai remains in a stable condition in Princess Alexandria Hospital with non-life threatening injuries.

Ms Wykes said Jai has Aspergers and would not take his medication.

"They just don't know what to do with him," she said.

The boy's grandfather, Jim Hunt, said the drama unfolded after the teen got into an argument with his father.

"My son (Nikolas) is all right; he has a scratch on him from the knife," Mr Hunt told The Courier-Mail.

"They were having a bit of a blue with each other. His dad was trying to control him."

Mr Hunt said his grandson was quiet and hadn't been to school in years, but that he had never been in trouble with police.

Australian Associated Press