A teenager is in hospital with severe burns after setting himself on fire while siphoning petrol from his car in Manurewa.

Fire Service shift manager Jaron Phillips said the 19-year-old was legitimately siphoning petrol from his own car last night in Foxlaw St, Randwick Park.

"He couldn't see what he was doing so used an open flame for some light. Either a cigarette lighter or a match."

A resulting explosion caused severe burns to most of his body. He is in Middlemore Hospital's intenstive care unit in a serious but stable condition.

"It was silly. He should have used a torch," Phillips said.

"It highlights the dangers of an open flame, even things like a candle at home when the power goes off."