Emergency services are warning Flat Bush residents to shut their doors and windows after a major fire that has left hundreds without power and closed down a major road.

A witness close to the fire said she “heard a bang” before the power in her shop cut out and smoke started to appear in the sky.

Police say a group of shops and a transformer were alight in Chapel Rd and there are concerns over the air quality from the smoke.

A Fire and Emergency spokesperson said the fire has since been extinguished, but four fire trucks remain on the scene as a precaution.

The fire has closed a major road and left homes and businesses without power.

Gaye Fisher, owner of Cocoon Thai Spa in Flat Bush, said the transformer made a large “bang” before the power cut out.

“I went outside and saw the smoke, and then the fire started,” Fisher told the Herald.

She said the power outage covered quite a wide area and firefighters had told her to stay inside and close her doors and windows.

Auckland Transport said on social media that Chapel Rd between Ormiston Rd and the southern end of Michael Jones Drive has been closed due to the fire.

“Avoid this area or expect delays with diversions in place affecting all traffic, including bus services,” the agency said.

A massive power outage has been reported as a result of the fire, stretching 6.7km down Chapel Rd. According to the Vector website, the outage was reported at 12.35pm and it is not known when it will be resolved.

A fire has left hundreds of homes and businesses without power in Flat Bush this afternoon. Photo / Vector