He was taken to Middlemore Hospital in a serious condition after emergency services were called about 8.30pm.
A St John northern communications shift manager said this morning the patient had burns to his arm.
Fire service northern communications shift manager Scott Osmond said firefighters were called to about a dozen fireworks-related incidents overnight but the Pukekohe incident was the only major event.
Southern fire communications shift manager Brent Dunn said he couldn't yet put a figure on the number of callouts his area had responded to, but said it was a busy night.
"There were quite a few fireworks calls, which we'd expect."
Selwyn, North Canterbury and Dunedin were the busiest areas for callouts, he said.
In the bottom half of the North Island, about half a dozen callouts were fireworks-related, fire's central communications shift manager said.