Mercury photographer Adam McLean was outside the court when the dramatic scenes unfolded on March 15, capturing the moment the man was intercepted by police and had his weapon seized.

Moments earlier, the man had tried to make his way into the courthouse - an attempt thwarted by eagle-eyed sheriff's officers manning the security screening point. 

A Sheriff's Office spokesman confirmed inquiries were under way.

"The Sheriff's Office is conducting an internal investigation after a man attempted to enter the courthouse with what appeared to be a prohibited item, but was later discovered to be a toy," the spokesman said.

"The man left the court without incident after being advised by a sheriff's officer that he couldn't bring the item into the building."

The Mercury understands the courthouse was not placed into lockdown and the man was not immediately detained by a sheriff's officer.

Questions to the Sheriff's Office, including whether standard safety protocols were followed, went unanswered. It would also not confirm reports an officer was disciplined for not arresting the man.

Sheriff's officers ensure the safety of judicial officers, legal professionals and the public in NSW courts.

The man was not charged in relation to the fake firearm, however, he did face court last weekend on separate charges of breaching an apprehended violence order.