An explosion inside a car that left a female with serious facial burns may have been caused by huffing, police say.

Police were called by St John Ambulance around 4.30pm today to a report of a car explosion on or near Campbell St in Frankton, Hamilton.

"We have had a notification from ambulance that the car door exploded after lighting a cigarette," a spokeswoman said.

She said a female had been sitting in the driver's seat when the explosion happened, leaving her with serious injuries.

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It appeared a person had been "huffing" - inhaling a gas such as butane - in the car before the explosion, she said.

An ambulance spokeswoman said she could not release details of the incident as it was classed as a medical event.