ELEANOR HALL: Multinational tobacco companies are coming under pressure today for their policy of buying tobacco from farms that exploit children.

An international study has revealed that children working in Malawi's tobacco fields are absorbing up a huge amount of nicotine, the equivalent to smoking 50 cigarettes a day.

Some of these children are less than five and they work for less than 2 cents an hour in oppressive conditions.

Jess Hill has this report.

JESS HILL: In the southern African nation of Malawi, if you're over the age of five, you're probably working on a farm. At least 78,000 children work on tobacco farms in Malawi. Working conditions are amongst the worst in the world.

Ian Wishart is the CEO of Plan International in Australia.

IAN WISHART: The children are really highly exploited. First of all, they're employed on very, very low wages; less than 2 cents an hour. That's less than 20 cents - 22 cents a day. If they're late for work or don't fulfil their quota they can be punished, both physically and sexually.

JESS HILL: A new study from Plan International has revealed that children working on tobacco farms are not just being heavily exploited, but poisoned by the crops they handle.

Forced to work without protective clothing, Malawi's child tobacco labourers absorb up to 54 milligrams a day of dissolved nicotine through their skin - that's the equivalent of smoking 50 average cigarettes.

Plan interviewed 44 children from tobacco farms in three districts. One teenage tobacco harvester, referred to as 'L', said it was common for him to feel breathless and vomit blood.

L (voiceover): Sometimes it feels like you don't have enough breath, then the blood comes when you vomit, you vomit blood.

JESS HILL: Malawi is the fifth largest producer of tobacco in the world, and Malawi tobacco is found in virtually every cigarette smoked in the West. Ian Wishart says that multinational tobacco companies are a big part of the problem.

IAN WISHART: I can't understand why these companies don't get it, but they've seemed to have paid scant regard to what we call their supply chain. I mean, even sports shoes manufacturers now take great pains to ensure their supply chain is clean.

JESS HILL: Child exploitation in Malawi's tobacco industry is nothing new. In 2001, British American Tobacco founded the Eliminating Child Labour in Tobacco Growing Foundation, or ECLT. Over four years, the foundation committed $US 2.2 million to community projects aimed at reducing exploitative child labour.

Marty Otanez is an assistant professor of political ecology at the University of Colorado. He's focused much of his research on Malawi's tobacco farms.

MARTY ORTANEZ: My research shows that they may spend up to $600,000 a year on these child labour projects, but they profit about $10 million per year from child labour and other non-paid labour.

JESS HILL: He believes that tobacco companies have a vested interest in maintaining the status quo.

MARTY ORTANEZ: The ECLT, I think it's representative of the tobacco companies' efforts to try to address some of the problems. But I think these organisations, and there's several, I think these are more about buying a reputation and a way to distract public attention from the real problems.

The real problems are their constant pushing the prices of tobacco leaf down as a way to sort of offset the loss of profits in affluent countries because we're smoking less. So they look to the farm end of the supply chain to try to reduce costs.

JESS HILL: Plan International's Ian Wishart says it's not realistic to call for a total ban on child labour.

IAN WISHCART: Plan is not arguing, indeed it can't argue it at this stage that these children should be immediately be taken out of these farms and therefore, they must be protected just as Australian workers would be protected.

JESS HILL: Marty Ortanez believes it's time for tobacco companies to become more transparent.

MARTY ORTANEZ: Can they commit to an independent monitoring group, not paid by tobacco companies, to assess the conditions on tobacco farms? Because I think that's something that they're you know, refusing to do, and I think that's a clear indication that they definitely do not want to be transparent.

JESS HILL: British American Tobacco would not be interviewed for this report but has issued a statement saying they support Plan International’s call for proper labour laws and that they would like to talk to them about their findings.

ELEANOR HALL: Jess Hill's reporting.