A couple critically ill from smoke inhalation had been burning charcoal to heat massage oil for their newborn grandchild.

The Papatoetoe couple were rushed to Middlemore Hospital late yesterday morning in a critical condition after burning the charcoal inside their Avis Ave home.

Son Tejendra Bhattarai told 1News his parents were using the burner to heat oil for his 6 and a half weeks old child.

The couple were found unconscious the next morning by his brother.

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"He rang me and said he had found vomit on the bed as well," he told 1News.

"I asked him to ring an ambulance and I'll be on the way."

Fire and Emergency NZ shift manager Daniel Nicholson said charcoal should never be used indoors, even if ventilation was available, because when it burned it produced significant amounts of carbon monoxide.

A St John spokeswoman said four ambulances attended the scene.