A motorbike rider has died after he crashed into a stray cow that was being herded off a northern NSW road.

Police were helping herd cattle off Casino Coraki Road near Casino in the early hours of Tuesday when the 51-year-old rider hit one of the cows, was thrown off his bike and into a parked police car.

Police say the man was treated by paramedics at the scene but declined to confirm where and when he died.