Clandestine cannabis growers in the Netherlands net two billion euros (2.7 billion dollars) a year, worth almost half the country's horticultural sector, a Dutch newspaper reported on Saturday.
By comparison, according to NRC Handelsblad, country's horticultural sector generates about 5.5 billion euros in annual income.
"There is major demand from England, Belgium, Germany, France, the Scandinavian countries and at the moment the Baltic countries," Max Daniel, the senior police officer who heads the Dutch agency charged with combatting cannabis-growing, told the newspaper.
Police investigations suggested that about 500 tonnes of Dutch cannabis were exported each year.
"We know that at least 80 percent of production is for export. In the Netherlands there are 400,000 users of the drug and of hashish. If it was only them, the problem would be entirely manageable," Daniel said.
"We still have the image of the small producer who grows a few plants in his attic to pay for his holidays in Benidorm (in southern Spain)," but the reality was quite different, Daniel told the newspaper, alluding to "professionals".
He thought the cannabis trade could be found behind most major murder, arms trafficking and drugs cases.
He quoted police sources as suggesting that banks were lending to growers, and that laboratories had ties to universities to increase production.
In July, the Dutch government set up a committee to examine and coordinate the fight against cannabis production, an activity in constant growth and increasingly professionalised.