A man has had his arm severed in a fireworks mishap south of Darwin, one of a series of incidents as revellers marked Territory Day.

The St John ambulance service said the 23-year-old was taken to Royal Darwin Hospital on Saturday night with an arm amputated below the elbow.

He was understood to have undergone surgery in a bid to have the arm reattached.

NT Health said he remained in a serious condition on Sunday.

A 58-year-old man suffered an injury to his groin in the same incident and was also treated in hospital.

He was in a stable condition.

The pair had reportedly been using a steel pipe to launch fireworks at a Virginia property.

But a misfire broke the pipe, scattering pieces of metal.

Police have established a crime scene at the site and investigations are continuing.

The fire service said crews responded to close to 100 calls on Saturday, many related to fireworks.

Chief Fire Officer Mark Spain said there were several incidents in the Darwin CBD and northern suburbs with people firing firecrackers at crews off balconies and roofs.

“Crews attended a structure fire at a unit complex on Smith Street last year and unfortunately attended the same complex again this year to warn residents who were firing crackers off the roof into the busy street,” he said.

By Tim Dornin in Adelaide