However, he believed the crash may have occurred at any time during the early hours of this morning.
"There's an indication that the crash happened prior to [St John] responding to it, so it might have happened at any stage during the night."
The man was taken to Waikato Hospital in a critical condition but he had since stabilised.
Their investigation is hampered as ambulance staff who attended the crash were now off duty. The Waikato police serious crash unit are investigating in case the man's condition deteriorates.
Meanwhile, Mr Ambler confirmed the man who died in a slow speed crash in Kihikihi on Wednesday suffered a heart attack while behind the wheel.
Although they're still investigating when the heart attack occurred, Mr Ambler said it's likely it happened prior to 55-year-old David Spence crashing into a bank on Te Mawhai Rd, near State Highway 3.
Mr Spence suffered injuries after being propelled into the windscreen as he was not wearing a seatbelt.