Police are investigating the deaths of six cows which were struck by a car and trailer as they were being herded across a Taranaki country road yesterday.

The 42-year-old driver and passenger, an eight-year-old boy, were taken to Taranaki Base Hospital where they were treated and discharged.

Farm worker Emil Dediu was herding the cows across the road at Waitara about 7am when he was forced to jump out of the way as the car ploughed into the cows, The Taranaki Daily News reported.

"It was horrible to watch. The first cow to get hit was thrown seven or eight metres through the air," he said.

"I have never seen cows flying through the air before."

New Plymouth police said the driver told them he had not seen the herd. The investigation was continuing.