Four men are dead and a woman is in hospital after a gunman opened fire with a pump action shotgun at five different locations in Darwin.

The 45-year-old suspected gunman, who was on parole and wearing an electronic monitoring bracelet, was arrested after being on the run for about an hour following the shootings in and around a hotel in the city's CBD on Tuesday evening.

Shots were first fired just before 6pm and the city was quickly placed in lockdown.

The alleged gunman was wearing hi-vis clothing when he fired 'up to 20 shots' at the Palms Motel on McMinn Street.

Emergency service vehicles were seen attending the scene in Darwin on Tuesday evening

The 45-year-old suspected gunman (pictured on the floor) was arrested after being on the run for about an hour

The initial shooting unfolded in the city's inner suburbs just before 6pm, but there are reports of up to five further crime scenes (police attending the scene pictured)

The female victim has been taken to the Royal Darwin Hospital in a stable condition and is currently being assessed.

Facebook user John Rose said he witnessed a man 'shoot up the Palms Hotel'.

'He was wearing high-vis, we found one person in the rooms that he shot up. Scary,' Mr Rose posted.

'We watched him like 20 feet away, calmly walk into the hotel room shoot the door open and then proceeded to shoot up every room,' he wrote.

Witness Leah Potter, who was at the nearby Alatai Holiday Apartments, said she saw a woman get shot.

Ms Potter told the ABC she had initially thought fireworks had been going off.

'I was in the carpark [of a nearby hotel] when I heard what I thought were fireworks going off, really loud cracking, banging fireworks,' she said.

'And then a man came running with a woman in his arms from next door which is the Palms Motel, which is the motel next to my motel, and he just dropped her on the footpath right in front of us.'

She said she tried to help the woman, who had 'little holes' in her skin on both legs.

Ms Potter added the victim was 'bleeding everywhere'.

The map shows four of the confirmed crime scene locations the suspected attended on Tuesday evening

Witness Leah Potter, who was at the Alatai Holiday Apartments (pictured) near to the city's Central Business District, said she saw a woman get shot

Another witness, who had been standing in the car park, said he saw a man carrying a wounded woman.

'There was this man carrying a woman towards me, put her in front of me and her legs were covered in blood,' he said.

'She obviously had been shot. So I went and got a towel for her. Wrapped up her legs. By that stage the police were running over.'

Another witness told the ABC he watched the man walk 'from room to room shooting every room'.

A third local said he had just got home from work when they heard a loud bang.

'[I] went to go out the front to check. As I've gone down towards the stairs I saw a guy in a high-viz shirt walk outwith a rifle and he looked at me and I ran into the bedroom and locked the door,' he said.

'We called the police and heard shot after shot after shot.'

Police confirmed the suspect then headed to a further four crime scenes.

Shots rang out at the nearby Buffalo Club, Gardens Hill Crescent, a Coles Express and Jolly Street in Woolner.

He also attempted to enter the Peter McCauley Centre facility.

Police could not provide a timeline of events on Tuesday night.

Police have confirmed a 45-year-old male is now in custody (Police attending the crime scene pictured)

It is believed two people were killed at the Palms Hotel.

Another witness said a man was shot in the head at a second crime scene on Gardens Hill Crescent – although police have not yet confirmed the reports.

A third crime scene was established at the Buff Club on Stuart Highway.

The daughter of the manager of the club said someone had been shot in the car park.

There were also reports, which have not been confirmed, that a man's throat was cut.

Police have confirmed four people have died and more a believed to have been injured (Ambulance officer near to the scene pictured)

The 45-year-old man was surrounded by armed police in the centre of an intersection on McMinn Street before he was tasered and arrested.

The man, who had no shirt on, dropped to the floor where he was apprehended by multiple officers.

The alleged gunman had been recently released from prison.

Police confirmed they are now trying to establish intent and motivation.

It's understood the alleged gunman was surrounded by armed police in the centre of an intersection before he was tasered (McMinn Street pictured)

Prime Minister Scott Morrison (pictured) has spoken out to condemn the 'terrible act of violence'

Prime Minister Scott Morrison has spoken out to condemn the shooting.

'This is a terrible act of violence that has already, I'm advised, taken the lives of four people. There are a number of others who have - casualties but the details of that is still not yet confirmed,' Mr Morrison said from London.

He said the matter would be 'managed' and 'dealt with' by the Northern Territory government.'

'I want to thank the Chief Minister (Michael) Gunner for the way that he's working with the Commonwealth authorities but particularly I just want to extend my deep condolences and sympathies,' he said.

Mr Morrison said the community in Darwin would be 'rocked' by the attack, but advised it was 'not a terrorist act'.

Chief Minister Michael Gunner (pictured) thanked the emergency services who attended the scene

'There is nothing to suggest that that is the case whatsoever. This is - the true motivations of this criminal and violent act will become better known.

'There is a person, I understand, in custody and they will work through those normal processes,' Mr Morrison said.

'In the meantime, I think it is important that everyone in Darwin, everyone in the Territory, understands that the thoughts of Australians, wherever they are, as far as away as where I am today or closer to home, they will be thinking very much of their fellow.'

Chief Minister Michael Gunner confirmed authorities do not believe the attack is a terror related.

Chief Minister Michael Gunner (pictured) at a press conference on Tuesday evening (Police Commissioner Reece Kershaw pictured right)

'This is not the Darwin we know. As Chief Minister, on behalf of Territorians, our thoughts are with the families and friends of the victim[s]and everybody else who has been impacted,' Chief Minister Gunner said.

'I understand when an event like this occurs, especially considering recent global events, people's fears turn to terrorism. I can confirm that we do not believe this is a terrorism incident.'

He went on to thank the emergency services who attended the scene.

'This may be an event you prepare for but this is never an event you want to respond to. I thank our police and first responders.

'This has been an incredibly difficult night tonight. Territorians can be proud of those who serve us on our front-line.'