Darwin shooting: Man arrested, multiple dead

Hoffmann, who was wearing an electronic monitoring bracelet, was arrested about 6.45pm in the Stuart Park area after an alleged hour-long rampage.

Four men were killed, while at least one woman was injured and taken to hospital for treatment.

Police believe the gunman acted alone and do not believe the incident was terrorism-related. They are still trying to establish the shooter's motive.

The shooting spree began at 5.45 at a motel in the suburb of Woolner, before the alleged gunman travelled to four other locations across the city.

Police arrested Hoffmann, known to his friends as "Hoffy", an hour later.

Television footage showed a man on the ground after being dragged from under a white dual cab ute, kicking his legs at officers from NT Police's Territory Response Group.

Hoffmann is being held in custody at Royal Darwin Hospital and no charges have been laid.

READ MORE: Darwin mass shooting: What we know so far

It's understood he was bashed two days before the shooting in Coolalinga, a suburb about 30 kilometres south-east of Darwin.

A former friend of Hoffmann, who did not want to be identified, said the alleged gunman had been in and out of jails for years.

"He was just a normal guy growing up but at some stage, maybe 15 or 16 years ago, we drifted to a normal life and he drifted to a life of drugs and crime. As far as I know, the last 15 years he's been in and out of jail," he said.

He said he last saw Hoffmann after he got out of jail earlier this year.

"He seemed normal. He was friendly. Happy to see me. I saw him again later but I avoided him, like you might do with people you know who are in and out of jail ...

"From what I've heard, since he's been out of jail he's been heavily into drugs."

Hoffmann's brother is Clinton Hoffmann, a successful businessman who is well-known in Darwin.

"His brother's a really upstanding citizen," said the friend. "He's mega successful. He's got a driving app and doing very well. He's often seen on red carpets and those sort of events. He's a good guy and I'm feeling for him tonight."

More than 100 police officers swarmed the city on Tuesday night to examine multiple crime scenes including the Buff Club, Palms Motel, a Coles Express and the Peter McAulay Centre police facility as they traced the shooter's steps.

Officers were able to track down Hoffman after he contacted a police duty superintendent, who alerted others to his location, NT Police Commissioner Reece Kershaw said on Tuesday night.

"He asked to be placed into protective custody, which we did," Mr Kershaw said. "We do believe he may have been trying to hand himself in. We're not sure."

Mr Kershaw said the suspected gunman had links to outlaw motorcycle gangs, was "well-known" to police and had had a number of "adverse interactions" with the force.

He said Hoffmann was released on parole about January this year after serving at least a year.

The incident started with reports of a man firing shots at Finnis Street about 5.50pm just outside the Darwin CBD, with the four deaths occurring at the nearby Buff Club, Gardens Hill Crescent, the Palms Motel and Jolly Street.

Witness John Rose told the ABC he saw a man walk into the motel with a "sawn-off shotgun".

"He shot up all the rooms and he went to every room looking for somebody and he shot them all up, then we saw him rush out, jump into his Toyota pick-up, and rush off," Mr Rose said.

Other witnesses said they heard what sounded like firecrackers. A woman told the ABC she saw a man with a shotgun, and gave first aid to a woman who had been shot in the legs.

Max Campart was having a drink at the Punters Bar, across the road from the Palms Motel, when he heard about seven or eight shots.

Patrons were told to move towards the back of the bar and stay away from the windows.

"We didn't know exactly what was happening. It was very loud," Mr Campart said.

While inside the pub, he glimpsed the alleged gunman walking down the street about 50 metres away.

"I saw a guy coming down the street in a white T-shirt with a gun in his hand," Mr Campart said.

Matthew James was standing in a car park nears the Palms when it all began.

"It was just surreal," he told Nine's Today program. "All of a sudden there were these gunshots.

"Moments later someone came running towards me carrying this woman who was covered in blood and just basically put her at my feet and she was screaming that she had been shot.

"The guy that actually carried her up was pretty frantic at the time, saying he had opened the door and there was a gunman there with a shotgun and he proceeded to fire upon anybody inside the building."

The woman was hysterical, Mr James said.

"She was caught up in it. She said, 'I've been shot, I don't know why, I don't have anything to do with anything,' he said.

The woman told Mr James the alleged gunman had been going from room to room, firing his gun and shouting the name "Alex".

"It just seems so insane," Mr James said.

Prime Minister Scott Morrison said the shooting was a "terrible act of violence" and said he had been in contact with police and NT Chief Minister Michael Gunner.

"I just want to send my deep condolences and sympathies to all the people in the territory and particularly in Darwin," Mr Morrison said from London.

"This is a very tight community and I know they will be rocked by these events.

"I think it's important that everyone in Darwin, everyone in the territory, understands that the thoughts of Australians [are with them]."

Mr Gunner said: "This is not the Darwin we know."

"On behalf of Territorians, our thoughts are with the families and friends of the victims and everybody else who has been impacted," Mr Gunner said.

"I thank our police and first responders."

Marietta Martinovic a criminology expert, from RMIT University, whose research specialises in electronic tag monitoring and reoffending said it was "extremely rare" for a suspect to commit a large-scale crime when wearing a monitoring bracelet.

"Most people that are put on bracelets are very aware of the fact and research shows that our highest risk offenders are least likely to reoffend while wearing a bracelet," she said.

Dr Martinovic said that, if the offender had been wearing a monitoring bracelet during the alleged attacks, authorities would have been able to track his moments in near real-time.

"It is extremely rare. Most people, before they decide to reoffend, they would certainly cut the bracelet off."

With Lisa Visentin, Nick Miller, Ben Weir, Georgina Mitchell and AAP