Four people are confirmed dead, and one is injured, after a shooting at a Darwin hotel.

Twenty gunshots from a shotgun were fired at approximately 5.45pm local time on Tuesday.

UPDATED: Here's everything we know about the Darwin mass shooting

It was 60 minutes of terror as a gunman reportedly moved between five suburban locations.

As he "calmly" went along his way he fired off many shots, according to witnesses.

Watch the video above.

Scene of deadly mass shooting in Darwin Credit: ABC News

NT chief minister Michael Gunner confirmed there were five crime scenes, four people dead, and one person injured.

"This is an active police investigation. There are a number of details still to be confirmed," he said.

Play Video The NT Chief Minister Michael Gunner and Police Commissioner Reece Kershaw have held a press conference. The NT Chief Minister Michael Gunner and Police Commissioner Reece Kershaw have held a press conference.

It was not a terrorist incident, he said.

The four killed were men, the one person injured is a woman.

One woman at a hotel on McMinn Street was shot multiple times in the legs with a pump-action shotgun, according to reports by the ABC.

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 witnessed the man walk through the hotel shooting 10 times and then get into his truck and drive away," he wrote in another comment.

Police on the scene of a deadly mass shooting in Darwin. Credit: ABC News

The alleged gunman has been described as being Caucasian, of approximately 195 centimetres in height and wearing high-vis workwear.

He reportedly fled the scene in a white Toyota Hilux ute minutes later.

The location of the hotel that the gunman fired upon. Credit: Google Maps

Northern Territory police quickly arrived on the scene and searched the nearby suburb of Woolner, five kilometres from the CBD.

A camouflaged tactical unit arrested, and possibly tasered, a 45-year-old man a short time later.

The five crime scene locations were The Buffalo Club, Gardens Hill Crescent, the Palms Hotel, at a Coles Express and at the Peter McCauley Centre, NT Police Commissioner Reece Kershaw confirmed.

At a Finniss St address, Kershaw said police seized a vehicle that the alleged shooter had attempted to move. Kershaw said the alleged offender asked to be placed into protective custody, but Kershaw would not say whether the attack was premediated or a random attack.

Kershaw said the man was on parole from January, and was believed to be wearing an electronic monitoring bracelet.

Kershaw said the man was taken to Royal Darwin Hospital.

He called on members of the public who may have more information or video of the incident to call NT Police.

Police response

Northern Territory Police Union President Paul McCue has been briefed on the situation and spoke to 7NEWS.com.au

"Obviously a terrible situation has unfolded here in Darwin tonight where it appears that a suspected gunman has taken the lives of several people," McCue said.

"Our thoughts certainly go to those deceased and of course to the first responders who have had to deal with that situation and are still dealing with it right now."

"Our information is that there are several people who are deceased but that investigation is still evolving at this stage and we're waiting on confirmation on that."

McCue said that the man's motivation remains unclear.

"Darwin is a pretty laid back relaxed place and no one would have suspected that something like this could eventuate here."

He also applauded the rapid response of police units.

"We're very grateful for the terrific work that our people have done up here this evening."

"They reacted immediately when calls began to come in and they were on the scene very quickly and resolved the situation as quickly as they possibly could given the horrific circumstances they faced."

The video below shows the emergency response to the shooting.

Play Video Emergency services have rushed to the scene of a mass shooting in Darwin this evening. Emergency services have rushed to the scene of a mass shooting in Darwin this evening.

Dramatic arrest

A woman living in Darwin city told 7NEWS.com.au she had no idea what was going on but “saw a whole heap of police cars driving towards the city”.

The 33-year-old, who doesn’t want to be named, took a video on of the man’s arrest from her high-rise apartment but didn't realise at the time it was related to the shooting.

Arrest in Darwin following mass shooting Credit: Facebook

She only found out there was a shooting after going onto social media and receiving calls from her family.

“My family were calling me to make sure I was safe,” she said.

Play Video Onlookers have captured footage of the alleged shooter being arrested. Onlookers have captured footage of the alleged shooter being arrested.

Prime minister comments

Prime Minister Scott Morrison, who arrived at an engagement in London on Tuesday, said he send his condolences to the people of Darwin and the Northern Territory.

Play Video The Prime Minister Scott Morrison has spoken briefly about the shooting in Darwin. The Prime Minister Scott Morrison has spoken briefly about the shooting in Darwin.

“This is a terrible act of violence that is already, I’m advised, taken he lives of four people,” Morrison said.

“I want to extend my deep condolences and sympathies to all the people of the Territory, particularly in Darwin. This is a very tight community and I know they will be rocked by these events.

“Our advice is that this is not a terrorist act. There is nothing to suggest that that is the case whatsoever. The true motivations of this criminal and violent act will become better known.

“In the meantime I think it’s important that everyone in Darwin, everyone in the Territory understands that the thoughts of Australians, wherever they are, (whether they’re) as far away as I am today or closer to home; they will be thinking very much of their fellow Australians in the Territory.”

Opposition leader Anthony Albanese said he had also been briefed.

Acting Prime Minister Michael McCormack tweeted his sympathies for the victims.

As did Northern Territory Labor senator Malarndirri McCarthy.

Watch the full press conference with NT Police Commissioner Reece Kershaw and NT Chief Commissioner Michael Gunner below.

Play Video The NT Chief Minister Michael Gunner and Police Commissioner Reece Kershaw have held a press conference. The NT Chief Minister Michael Gunner and Police Commissioner Reece Kershaw have held a press conference.

- With AAP.