The lamp post fell on to power lines.
The car was left up against the base of the lamp post. After initial reassurance the man was told to stay in the Toyota two-door vehicle while emergency workers stood back.
Whangarei Fire Service senior station officer Paul Thompson said until it was confirmed the power supply was off they could not move in.
"We had to wait. It's very stressful to see someone obviously in a bit of difficulty but we just can't risk the lives of others," Mr Thompson said.
Northpower was notified of the crash at 9.58am. A senior staff member went to the site four minutes later and was in touch with the company's control room.
Spokesman Steve MacMillan said if a vehicle was regarded as "live", crews are instructed not to go near or touch the vehicle because they could be electrocuted, as could emergency crews.
He said in yesterday's case the 11kV line had to be isolated and earthed which could not be done until field staff had completed the switching under control's instructions, which is standard industry practice.
"The line staff doing the switching were outside of the immediate area, working in surrounding streets doing the switching, to make it safe for the other crews to isolate and earth," Mr MacMillan said.
At 10.34am the site was made safe and emergency workers were given the all clear to go in.
St John ambulance officers and firefighters quickly opened the car door and talked with the man before lifting him on to a stretcher and loading him into an ambulance in a serious condition.
He was taken to Whangarei Hospital where he remained late yesterday.
The crash caused a power cut to Whangarei Hospital and 900 customers.
The hospital switched to a generator until 10.13am when power was restored along with 580 customers. It was fully restored just after midday.
