An elderly couple on their way home from Taranaki's Americarna festival have suffered horrific injuries in a crash caused by a tourist driver.

Auckland couple Anne and Martin, who are both in their 70s and whose family requested their surname not be used to protect loved ones from knowing the full extent of their injuries, were driving their 1939 Chevrolet Master Deluxe coupe north on State Highway 31 near Otorohanga on Sunday morning when an American driver suddenly turned in front of them.

They had no time to stop and slammed into the tourist's car.

Anne suffered a fractured spine, broken nose, six broken ribs and needed 10 stitches in her eyebrows, while Martin's front teeth were smashed upward into his skull. Their injuries were particularly bad because the classic car did not have seatbelts or airbags.

The 75-year-old American tourist and his passenger had been in the country just two days and were heading from Auckland to Waitomo Caves, using a GPS to navigate. They suffered only minor injuries.

The Auckland couple's son, Warren, said it was another instance of a tourist driver causing a crash, reinforcing the need for better education about New Zealand roads before they got behind the wheel. America's user-friendly roads were vastly different to New Zealand's, he said.

"I'm not happy with tourists coming and being able to rent and drive a car without being given the appropriate skills to drive here."

Warren said the American driver and his companion, who were Vietnam veterans, were far from negligent.

"I feel a degree of sadness for them, their holiday has been ruined," he said.

"Clearly they were not equipped to deal with driving on our side of the road and our open road conditions.

"Unfortunately they've taken out a precious historic car and almost my parents."

The latest crash comes on the back of a spate of tourist-related road crashes around the country.

These include one involving Frenchman Stephane Yuan Mazerat, 29, who admitted three charges of dangerous driving causing injury after a crash at Awakino on January 5.

Five overseas drivers appeared in Otago courts last week facing charges related to causing death and injury on southern roads.

The American tourist pleaded guilty in the Hamilton District Court yesterday to two counts of careless driving causing injury and will be sentenced later this month. Warren said his parents were still in a bad way in Waikato Hospital and would recover eventually but the car they had spent tens of thousands restoring was likely a write-off.

He said emergency services arrived within 10 minutes.