The owner of the Netherlands' biggest cannabis-vending coffee shop went on trial for drug trafficking Tuesday accused of storing more than the allowed amount of the soft drug on site.

Meddy Willemsen, 58, was not present for the opening of his trial in Middelburg in the southern Netherlands which is widely seen as a test case in a country that has been toughening its stance on soft drug use.

- The question is whether the conditions of the government's tolerance policy have been violated - presiding judge Saskia Meeuwis said at the start of the trial.

Though technically illegal, the Netherlands decriminalised the consumption and possession of under five grammes (0.18 ounces) of cannabis in 1976 under a so-called "tolerance policy".

Cannabis cultivation and mass retail remain illegal and are in the hands of criminal organisations in a black-market business worth some two billion euros (three billion dollars) per year.

There are around 700 licensed coffee shops in the Netherlands which are allowed to keep no more than 500 grammes of cannabis on their premises, though this limit is often flouted.

In this case, investigators claim to have found 120 kilogrammes of cannabis on the premises of Willemsen's Checkpoint coffee shop in Terneuzen near the border with Belgium in 2007, and another 110 kilos last year.

Before it was closed in May 2008, Checkpoint counted up to 3,000 clients a day, mainly Belgian and French, allegedly earning Willemsen more than 27 million euros between 2006 and May 2008.

- This is clearly a contravention of the spirit of the tolerance policy devised (by the government) to respond to local demand - Middelburg prosecution spokeswoman Elke Kool told AFP.

Willemsen stands accused alongside 16 others, including a manager of his coffee shop and local suppliers. All but one, a 37-year-old supplier, were absent on Tuesday.

A verdict in what prosecutors describe as the biggest-ever case of its type in the Netherlands is expected on December 2.

The Netherlands has recently been taking an increasingly tough stance on recreational drug use, citing what critics see as a nuisance created by millions of drug tourists who cross the border every year.

The government announced plans in September to limit drug tourism by reserving hundreds of cannabis-vending coffee shops for locals.

The capital, Amsterdam, has said it will halve its number of coffee shops, citing criminality, while other cities are to close shops within a certain distance from schools.

In the southern Limburg province, 30 coffee shops intend to become private members' clubs from next year.