St John Ambulance spokesman said the man was taken to Auckland Hospital in a critical condition.
Local resident Andrew Rutland said his daughter Amy, a nurse at Waitakere Hospital, helped treat the man after finding him lying in the road.
"She was just trying to stop the blood," Rutland said. "They wrapped blankets around his head and offered basic assistance. You can only hope that it helped."
Local resident Jaydene Kukard said the a tight corner and fast-flowing traffic near the crash spot made it dangerous.
"I've seen people crossing the road while people are gunning it around the corner," said Kukard.
"I do think they should do something about it."