Police say they have busted the first known New Zealand lab producing a date-rape drug known as "coma in a bottle".

Armed police raided a Huntly house this week, allegedly finding an operation set up to make the class B drug gamma-butyrolactone (GBL).

It was believed police were alerted to the lab when the men involved bought large quantities of a fungicide normally only used against crop diseases in the South Island, the Waikato Times reported.

Four men, Marc Patrick Johnson, 46, Allan Joseph Ellison, 49, Steven Meli Herman, 40, and James Hill Damian Worthington, 48, appeared in Hamilton District Court on Wednesday charged with producing the drug, and two counts of possessing equipment for its manufacture.

The four remain in custody.

GBL - also known as fantasy or rinse - had gained popularity as a party drug in Europe and the US.

It can be mixed with water or orange juice, and is said to produce a high similar to ecstasy.

However, the concentration has to be measured precisely or the user can end up unconscious or dead.

Police prosecutor Brendon Bland said GBL had been imported before, but the alleged Huntly lab was the first of its kind.