The tobacco industry wants the government to crack down on what it says is a burgeoning black market in homegrown tobacco.

The tax on cigarettes over the next four years leading to a 50 percent price hike will spark an explosion in the illicit tobacco trade unless action is taken now, the industry says.

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British American Tobacco said it has evidence of a thriving black market in homegrown tobacco, including footage of plantations being grown near Motueka.

Its spokesperson Saul Derber said processed homegrown tobacco finds a ready market among those wanting to buy tobacco 40 to 70 percent cheaper than legal tobacco.

"We see an increase in activity on Trade Me, anyone can go and have a look and you'll see trade in seeds and plants, that's increasing, but even more worrying... is the increasing prevalence of these closed secretive Facebook and other social media groups where illegal homegrown is traded."

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The law allow people to grow tobacco for personal use and individuals can process 15kg a year, equivalent to 90 cigarettes a day.

Nobody can smoke this amount and the law is only encouraging its illicit trade, Mr Derber said.

He wanted those growing their own to be subject to the same taxes as commercial manufacturers.

"If legal companies are expected to pay 77 percent of the price of a pack to the government in various taxes then so should people growing it in their own back yard, because at the end of the day the health consequences with tobacco are the same whether it's homegrown or whether it's manufactured."

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Homegrown sales have increased since the price of commercial cigarettes started rising, said Darren Chubb, who sells tobacco seeds on Trade Me.

"We were selling about a bag a month but now we're selling two bags a week, all of a sudden, it was unbelievable, it was like turning on a switch."

But homegrown tobacco was not about to knock the multi-billion-dollar tobacco industry off its perch, he said.

"It's too much labour involved in getting it right. If you're smoking, let's say a packet a day, it'd be pretty hard work to produce that much unless you were a retiree or something like that."

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Another grower, who asked not to be named, said she grew her own because she preferred organic tobacco and wanted to avoid the additives the big companies include in their products.

The most important part of the process was curing the tobacco, she said.

"They have a high chlorophyll content and to get that out you would ferment them. So you'd pick them, let them dry and ferment them. So I just turned an old fridge into a fermenter, I put a rice cooker in there that created the right moisture content."

Action on Smoking and Health (ASH) spokesperson Stephanie Erick said the industry was talking up the threat posed by those growing their own tobacco as a distraction from the part it plays in promoting smoking.

"It's also about undermining the plain packaging and other legislative measures that we're trying to work towards. They use scaremongering tactics like telling us that illicit trade is going to hit the roof where actually in New Zealand it's less than 4 percent, it's very small."

A 2014 report from the Ministry of Health recommended the amount of tobacco a person should be allowed to process for personal consumption be reduced from 15 kilograms to just 5 kilograms, but so far there has been no change to the law.