Rescuers risked their lives to pull a driver from his wreck after he smashed into a power pole, snapping it half and causing live wires to fall over the vehicle.
But power company Vector are urging people to not to do the same in future.
Residents of Russell Road in Manurewa raced from their homes after hearing the crash as a four-wheel drive Isuzu collided with a corner concrete pole about 4pm, ripping it from the ground and flipping the vehicle on its roof.
Mike Pennot was one of those and said they helped the driver trapped in the crumpled wreck even though electricity wires draped the vehicle.
"The driver's back was sticking out through the window so I asked if he was alive and he groaned."
There was a lot of smoke coming from the engine so those who had raced out decided to try and get him out, Pennot said.
"I could see the power line was still insulated so I lightly touched the vehicle."
He said a number of attempts to pull the injured man to safety was unsuccessful and he wasn't freed until emergency services arrived.
A Vector spokeswoman urged people to leave such rescues to emergency services.
"Vector is concerned that people... may think it's safe to try and rescue people in vehicles that have crashed into power poles and live lines have come down," she said.
"We advise that all lines should be treated as live at all times and that people must leave these situations to the emergency services."
Senior Sergeant Ian Brenchley said just before the crash police had been contacted by motorists concerned the driver had been drinking.
He said when an officer went to speak to the driver he appeared to be drunk.
"The cop tried to stop him from driving off and get the keys," said Brenchley.
However, the driver argued with the policeman and drove off, he said.
Moments later calls flooded emergency services about the crash which involved the same vehicle and driver.
The man was taken to Middlemore Hospital with life-threatening injuries.
Vector teams are tonight working to repair the damaged wires and pole.