A NEW Zealand man is in a critical, but stable condition after crashing a motorised bar stool north of Auckland.

The man, 62, had just left the Puhoi pub on the recreational vehicle - a go-kart with a bar stool on top - when he fell on Friday afternoon.

He was driving on the road without wearing a helmet. No other vehicles were involved, police say.

The man was airlifted to Auckland City Hospital with serious head injuries.

He was in a critical, but stable condition on Saturday afternoon, a hospital spokeswoman said.

Inspector Mark Fergus on Friday said police were investigating whether alcohol contributed to the crash.

"The vehicle was not road-legal and we've seized it so it can be mechanically examined," he said.