Police are looking into whether NSW Police Minister David Elliott broke the law, after a photo surfaced of him firing a submachine gun at a rifle range for prison officers.

Key points: The fully automatic weapon is illegal in NSW, except for use by the Army and some police and corrections officers

The fully automatic weapon is illegal in NSW, except for use by the Army and some police and corrections officers It is understood the police probe will determine whether special forms were signed before Mr Elliott used the weapon

It is understood the police probe will determine whether special forms were signed before Mr Elliott used the weapon Greens MP David Shoebridge said it showed a lack of judgment from the Minister in charge of law and order

It was one of a series of pictures posted on Mr Elliott's official Facebook page in September 2018 to mark the opening of the range at the John Morony Correctional Centre near Windsor in Sydney's north-west.

The Opposition says Mr Elliott, who was corrections minister at the time, should be stood down over the allegations.

In one picture, Mr Elliott is holding the fully automatic weapon and firing at a target, while in another he is taking aim with a pistol.

The matter is now the subject of a police inquiry to determine whether the Firearms Act has been breached.

Submachine guns are illegal in NSW, except for use by the Army and some police and corrections officers.

Those without a specific licence are required to sign a series of forms prior to firing the weapon at a shooting range.

It is understood the police probe into Mr Elliott's actions will centre on whether the documentation was completed.

The Minister's office initially would not comment on the matter, instead referring the ABC to Corrective Services NSW (CSNSW).

However, in a statement Mr Elliott said he fired the weapons "under the strict supervision of the range master".

"I acted in good faith under the assumption that CSNSW had complied with all of its administrative requirements according to the Firearms Act," the statement said.

Mr Elliott said he was told that he "and potentially hundreds of individuals" who had used the range were potentially in breach of the act.

"Given the safety and security of firearms is of the utmost importance to me, I immediately asked the Police Commissioner to investigate the operation of the CSNSW firing range to ensure they comply with the relevant legislation governing the use of firearms within their training establishments."

Mr Elliott also fired a handgun at the facility. ( Facebook )

Labor MP Lynda Voltz questioned what Mr Elliot was doing on a rifle range if he did not know the laws around firearms.

"He's the Minister for Police. He can't just come along and say, 'Well, you know, despite having been in the army, despite being Minister for Police, I didn't know what I was doing.'

"[He was] up in the Parliament just last week amending the firearms act.

"I don't know what it takes to get this minister with a long list of indiscretions stood aside, but the Premier should stand him down."

Corrective Services NSW has issued an apology to the Minister for "any embarrassment caused" at the weapons range as well as any suggestion he had done something wrong.

"At all times ... the former minister was acting on the advice of Corrective Services and under the direction of a qualified weapons instructor," a spokeswoman said.

"As a result of media inquiries, Corrective Services has referred its actions at the range to the NSW Police Firearms Registry to ascertain if an administrative error has occurred."

In a statement, NSW Police said the Minister contacted Police Commissioner Michael Fuller on Sunday in relation to "concerns over the conduct of the shooting range".

"The matter will now be referred to an appropriate command in order that further inquiries can be conducted," the spokesperson said.

The rifle range is designed to provide specialised firearm training for prison officers.

The now Police and Emergency Services Minister is likely to face a grilling today as he is scheduled to face a budget estimates hearing.

"Minister Elliott has very serious questions to answer," Greens MP David Shoebridge said.

"We have tough firearms laws in this state providing hefty criminal penalties if you are holding or operating a firearm without an appropriate licence and I'd invite him to put on the record if he held such a licence."

Mr Shoebridge said it also showed a lack of judgement from a Minister in charge of law and order.

"You'd have to wonder what is going through the mind of a senior Minister … to go and pick up a lethal weapon like this without checking if they had a lawful capacity to do that," Mr Shoebridge said.

Mr Elliott was already expected to face some uncomfortable questions at the budget estimates hearing over his decision to leave the country on a European holiday when bushfires were blazing across the state.

His refusal to cancel his trip came less than a week after the furore over the Prime Minister's Hawaiian holiday. Ultimately, Elliott decided to cut his holiday short.

The Minister has also been the subject of a NSW Police review after a 17-year-old P-plater alleged Mr Elliott grabbed his arm and chased him through the streets after a minor car crash last October.

Mr Elliott denied the allegations and the review found "no further police action" could be taken.