A Charles Sturt University (CSU) policing and security expert says it is time for the government to consider another gun amnesty and buy-back scheme in Australia.

Head of the CSU Australian Graduate School of Policing and Security, Associate Professor Nick O'Brien, said the amount of illegal firearms in circulation in Australia, and the fact that they are regularly used in crimes, indicates that there is a strong possibility of a mass-casualty gun-related tragedy occurring again in this country.

"In addition to the use of guns in conventional crimes, there is also the possibility of them being used in terrorist acts as happened in Lindt Cafe siege in Martin Place, Sydney, in December last year," Professor O'Brien said.

He noted that the Joint Commonwealth-New South Wales Review of the Martin Place siege estimated that there are 250 000 illegal firearms in Australia.

"That represents one illegal firearm for every 88 people in Australia," he said.

"Furthermore, the Australian Crime Commission, 'conservatively estimates that there are more than 250 000 long-arms and 10 000 handguns in the illicit firearm market'.

"And as recently as today, the Secretary of the Victorian Police Association, Mr Ron Iddles, has stated that police in Victoria are finding guns every two days and that there is a gun-related crime every six days."

Professor O'Brien said that in the aftermath of the 1996 Port Arthur massacre in Tasmania the government instituted a gun buy-back scheme which lasted from October 1996 to September 1997 during which 700 000 guns were handed in to police.

"In the ten years prior to the Port Arthur incident there were 11 mass shootings - defined as involving five or more people - in Australia, and since the buy-back amnesty there has been none," he said. "The government, the community and law enforcement authorities need to remain vigilant and proactive to minimise the risk of gun-related crime and tragedies.