Police are offering cash rewards for anyone who provides information which leads to the prosecution of those selling black-market tobacco.

Police launched the month-long campaign late last month in response to rising violent robberies targeting small businesses.

The campaign is being advertised on social media and informants are being asked to contact Crimestoppers with information about those peddling stolen goods.

The campaign, titled "There's nothing good about stolen goods", comes as Dunedin police continue to investigate the gunpoint robbery of Halfway Bush Convenience Store on May 2.

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A man entered the store shortly before 11am and pointed a rifle at the shop attendant. He stole cash and tobacco before fleeing.

A police spokeswoman confirmed no-one had been arrested in relation to the robbery.

Police would not discuss the specifics of cash rewards being offered, but said "the amount would vary depending on each circumstance".

"It will be when information leads to successful prosecution," the spokeswoman said.

Police would not say if rewards had been offered under the campaign, citing "confidentiality and operational reasons".

The most recent police statistics show aggravated robberies in the Southern district have risen by more than 25 per cent in the past year.

Speaking at the campaign's launch, police commissioner Mike Bush said it was hoped the campaign would make a dent in the number of violent robberies driving the black market trade in tobacco and stolen goods.

"NZ Police are deeply concerned about the rise in this violent crime due to its significant impact on small-business owners and their workers and communities," he said at the time.

To be eligible for a reward, you would need to provide your details to Crimestoppers when you called, Bush said.

The campaign is scheduled to finish at the end of this month.