"Act says it will not be illegal for a shopkeeper to keep a weapon in their own shop."
The possibility that a shopkeeper was armed would deter would-be offenders, Dr Whyte said.
The party would also strengthen laws relating to self-defence and introduce a dedicated home invasion law.
Dr Whyte said he had no view on what weapons shopkeepers should arm themselves with but believed firearms were appropriate, "if they felt that there was sufficient threat".
The idea was dismissed by Prime Minister John Key this afternoon.
"The reason I think it's a bad idea is that firstly you'd be putting weapons in the hands of people that are not trained," he said.
"Those weapons could be used [against] the very shopkeepers themselves. It's a recipe for disaster."
New Zealand Association of Convenience Stores chairman Roger Bull said the association did not support shopkeepers arming themselves.
"Our policy has always been if there's a robbery, you comply with the instructions of the person and you do not try to do anything quick or sudden because you don't know the mental state [of the offender].
"You comply and get them out of the way as quick as possible."
Currently under the Crimes Act, "Everyone is justified in using, in the defence of himself or herself or another, such force as, in the circumstances as he or she believes them to be, it is reasonable to use".
Police Association president Greg O'Connor said introducing "stand your ground-type laws" would benefit criminals more than law-abiding citizens.
"The law is not that much of an ass, nobody in New Zealand is going to be convicted of an offence where it is quite clear that they were acting in self-defence.
"That doesn't happen and it's not going to happen. Really, it's not as big a problem as it's probably being made out.
"Once dairy owners start having firearms, major issues [arise] because I don't think New Zealanders are ready for a dairy owner to shoot a shoplifter, but that's what will end up happening."
Labour leader David Cunliffe dismissed the policy as "an extreme Tea Party-type policy" that had no place in New Zealand society.
"We don't want vigilantes, we want a police force we can rely on."
Auckland barrister Gary Gotlieb said current self-defence legislation was sufficient and it was questionable that such a "populist" policy was coming out a week before the election.
Victoria University criminology lecturer Trevor Bradley said violence was not an answer to violence or the threat of violence.
Sensible Sentencing Trust spokeswoman Ruth Money said the organisation supported a review of current self-defence legislation but didn't want to see "a crazy increase of firearms behind every counter".
