The father of Australian gun control says it's simplistic and flawed to believe weaker gun laws could have prevented the Martin Place siege.

But John Howard says he's not looking to get into a debate with the crossbench senator, David Leyonhjelm, who's blamed tight gun controls for creating "a nation of victims".

Senator Leyonhjelm is calling for the laws to be watered down, saying the deadly siege in the Lindt cafe wouldn't have happened if patrons could have had concealed weapons.

"That nutcase who held them all hostage wouldn't have known that they were armed and bad guys don't like to be shot back at," he said.

Cafe hostages Tori Johnson and Katrina Dawson were reportedly shot by Man Haron Monis moments before police stormed the shop and killed the gunman.

"It would have been illegal for them to have a knife, a stick, a pepper spray, a personal Taser, mace, anything like that for self-defence," said Senator Leyonhjelm.

NSW Police are seen in Martin Place near the Lindt Cafe in the Sydney CBD. (AAP)

"To turn an entire population into a nation of victims is just unforgivable."

But former prime minister Howard remains certain the laws he enacted after the Port Arthur massacre had made Australia safer.

"It's just an exercise in logic to understand that the more guns there are in the community, the greater the likelihood of mass murder," he told ABC radio.

Senator Leyonhjelm quit the Liberal Party in disgust at the 1996 laws, and has also been a member of the Shooters Party.

Mr Howard said the Liberal Democrat's stance was "a very simplistic and flawed analysis".

"It's very important in the wake of that terrible event for us to keep calm and understand what the right responses are," he said.

Armed officers talk on Phillip St close to Martin Place. (Getty)

"I don't think a right response is to make guns more freely available in the community."

Gun control expert Philip Alpers, from the University of Sydney, said the US was suffering from an epidemic of gun deaths. By contrast, the rate in Australia had halved since laws were toughened.

Current political leaders have also criticised the senator.

NSW Premier Mike Baird had one word for Senator Leyonhjelm: "Wrong".

"That is outrageous," he said.

"I couldn't think of a (more) inappropriate comment than that."

The first hostage exits the cafe at Martin Place. (Seven Network)

Both Attorney-General George Brandis and Opposition Leader Bill Shorten said the question wasn't whether laws were tough enough but if they were being properly enforced.

Senator Brandis said it appeared the type of gun Monis used was banned under the 1996 laws, although he cautioned the need to wait for the full investigation to be sure.

"If the weapon he had indeed was a banned weapon, then there's only one way he could have got that weapon and that is illegally," he told ABC radio.

Mr Shorten couldn't see how putting more guns in the community would make Australians safer.

Senator Leyonhjelm has taken to Twitter to defend his comments, calling his critics "hoplophobes" - afraid of guns.

"In which being killed by a lunatic is preferred to having the means to save your own life," he tweeted.

© AAP 2014