ABC reports the gunman has been arrested.
Witness John Rose told the ABC the gunman walked into Palms Motel on 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."
UPDATE: NT chief minister Michael Gunner has 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.
"It was not a terrorist incident".
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.
The four killed were men, the one person injured is a woman.