Police were called to a Forest Lake home about 3.20am on Sunday before finding the boy on the street on Banksia Circuit following reports of a disturbance involving an armed person.

The boy armed with knives was allegedly threatening police before shots were fired.

Superintendent Tony Fleming said both officers, including a Senior Constable, fired their weapons.

"Unfortunately during the engagement with that young man, it was necessary that the officers, fearing for their safety, felt it necessary to discharge their weapons," he said.

Superintendent Fleming said the officers performed first-aid to the teenager while calling for paramedics and back-up, with other officers assisting the injured boy.

"During the course of that, one female officer who was rendering assistance to the young man will allege that the young man continued to resist and she suffered an injury, possibly a broken arm, despite trying to assist him," he said.

The teen was taken to the Princess Alexander Hospital with abdominal injuries and was expected to undergo surgery.

Superintendent Fleming described the incident as a tragedy for the teenager and his family as well as the officer involved.

"Police have certainly got the equipment and are dealing with dangerous situations every day but none of them ever want to come to work and ever have to discharge their firearm," he said.

Superintendent Fleming said the officers would be under "scrutiny in discharging their weapons" as part of an investigation into the incident.

"They’re OK but [it is] obviously a very distressing situation for them," he said.

"They are now going to go through significant scrutiny for what happened ... they were on their way to help people and this has unfortunately unfolded for them and this young man.

"It is a tragedy for everyone involved."

The Ethical Standards Command has begun an investigation into the incident, which will be over-seen by the Crime and Corruption Commission.