Fire crews were called to a house on Latham Ave, in Pakuranga, shortly before 2pm following reports of multiple explosions in the area.
Northern fire communications said they could hear explosions over the phone as they took calls from the public.
Witness Keith told Newstalk ZB he arrived about five minutes before firefighters arrived and saw several explosions coming from the garage.
"When the garage was exploding you couldn't get near the house because it just exploded straight across the road. There was one lady lying on the ground how the lady was attending to.
"The garage is completely gone now and part of the front of the house is all burnt out."
It is understood chemicals or gas were likely involved in the explosion, but there was no indication at this stage that drug manufacturing was a factor.
A New Zealand Herald photographer at the scene said the fire took place in a double garage in front of a house.
The remnants of a vehicle could be seen inside the garage, which was left charred.
Firefighters are still at the scene and were walking around the property hosing down hot spots.
Authorities have also put up a large cordon around the area and have blocked access to a part of the road.
A worker at the nearby Pakuranga Liquor store said he saw large plumes of smoke coming down the street at about 2pm.
Duty manager Sarbjit Singh told the Herald: "We could see the black smoke -- so much smoke. I think the whole house is gone."
Mr Singh said he did not know if anyone had been injured in the blaze, but could see people standing on the street.
"People have come out of their houses."
Another resident said she was driving down Pakuranga Road with her daughter when they saw flames.
"We could see the black smoke blowing out and could see the flames. It's probably about three houses across from where we are," the woman, who did not want to be named, said.
A specialist fire investigator is working to determine the cause of the blaze.
