Growers had converted a 250-square-metre warehouse into a greenhouse and were growing some 3,000 marijuana plants, a police spokesperson said. The harvested pot would have been worth €500,000 on the black market.

Four alleged growers aged 26 to 40 led police on a chase through a prepared getaway in the building’s cellar, but were caught and arrested outside.

Anonymous reports in recent weeks tipped off authorities to the marijuana plantation, they said.

Officers confiscated growing lamps, ventilators and other materials worth some €100,000 from the warehouse, all of which had created “optimal conditions” for growing the weed.

One of the people arrested, a 40-year-old man from the Netherlands with a residence in Hohenstein, Thuringia, is considered to be the ringleader and is set to go before a judge by Tuesday evening.

Meanwhile two Polish men, aged 36 and 40, and a 26-year-old German from Ellrich, Thuringia were considered “harvest helpers,” and were released from police custody as the investigation continues, police said.