It is used like a gun, looks like a gun and scares like a gun -  except it is perfectly legal to buy at toy stores.

Replica firearms were used in 42 armed robberies across the state in the past five years and continue to be sold without any restrictions because of a gap in gun laws.

Police have recorded 394 incidents involving fake firearms in the same period, and 90 of those involved violence, according to the Bureau of Crime Statistics and Research.

The figures comes after Fairfax Media reported a 10 per cent surge in gun ownership across NSW, bringing the total number of legally registered firearms to 850,636.

South-western and western Sydney recorded some of the highest rises in gun ownership with 4689 firearms registered in Liverpool; 4505 in Chester Hill followed by 4442 in Horsley Park.

Greens MP David Shoebridge said replica firearms were just as intimidating as real guns and should not be able to be bought in  toy stores or at markets.

At present, no matter how real a replica gun looks, it can still be sold legally.

"Most gun crime involves a gun being used to intimidate rather than shoot someone," Mr Shoebridge said.

"Unfortunately, realistic replica firearms are just as good as the real thing when it comes to intimidating and frightening people.

"This is not about fluorescent Nerf guns, it's about properly regulating replicas that are authentic enough to rob a service station."

Deputy Premier and police minister Troy Grant did not comment on whether changes to legislation needed to be made but said anyone who used a replica gun faced criminal charges.

"Anyone who uses a firearm, real or otherwise, to carry out a crime is committing an armed criminal offence and will face the penalties under the law," a spokeswoman said.

In March, police arrested a man who allegedly went on an armed robbery spree wearing a surgical mask before he was arrested for brandishing a replica gun near the Lindt Café in Martin Place.

Police charged Tianyye Hu, 54, with eight counts of armed robbery with a dangerous weapon after he allegedly targeted people and businesses with a fake gun over five weeks.

The incident came just nine days after the Lindt cafe was reopened following the siege which left Lindt cafe manager Toris Johnson, 34, and lawyer Katrina Dawson, 38, dead.