Northern Territory police say a party trick with a firecracker has left a Darwin man with severe burns to his buttocks.

Watch Commander Garry Smith says police were responding to reports of firecrackers being let off in the suburb of Rapid Creek on Saturday night.

He says police were conducting patrols when they were flagged down by people requesting an ambulance.

"It appears that a party was in full progress when a young male decided to place a firework between the cheeks of his bottom and light it," he said.

"What must have seemed to be a great idea at the time has obviously backfired and resulted in the male receiving quite severe and painful burns to his cheeks, back and private bits."

The man was taken to Royal Darwin Hospital.

Fireworks can only be let off in the Northern Territory on July 1 to celebrate Territory Day.

"I just remind people, they face a $282 fine on the spot for possessing and discharging fireworks outside of that designated period," Commander Smith said.

"And apparently they're not designed for that particular placement."