Officers have intercepted 12 kilogrammes of the drug, public broadcaster Polish Radio’s IAR news agency.
They found 8 kg of marijuana inside an Opel, and a combined 4 kg in a Volvo and a Fiat brought by another truck, the IAR news agency said.
The truck drivers hired to transport the passenger cars to Poland probably had no knowledge of the hidden cargo, according to police.
The investigation is ongoing and further detentions may follow, Poland’s Central Bureau of Police Investigation (CBŚP) has said.