A teenage boy is one of two people arrested after a joint operation between NSW and Queensland police targeting an alleged cross-border drug ring led to the seizure of more than 20kg of methylamphetamine and hundreds of thousands of dollars in cash.

NSW Police found 20kg of a substance they believe to be methylamphetamine inside a Hyundai Santa Fe on the Pacific Highway near the Mid-North Coast town of Nabiac on Monday.

The 26-year-old driver of the car was arrested following the search and taken to Foster Police Station.