Northern Territory Police confirmed on Facebook that a man was a taken into custody and that there were also "multiple injuries and multiple crime scenes."
The Australian Broadcasting Corporation (ABC) reported that witnesses saw the man walk into Palms Motel in Darwin holding a sawn-off gun and open fire on a number of rooms.
“He shot up all the rooms and he went to every room looking for somebody and he shot them all up,” witness John Rose told ABC.
“Then we saw him rush out, jump into his Toyota pick-up, and rush off.”
Police say it is not believed to be a terror-related incident.
Australian media reported that the gunman then moved to other areas of Darwin. Large sections of the city, which has a population of 100,000 were closed down while the police operation took place.
Police earlier said the suspect was wearing a high-visibility shirt and driving a Toyota pickup truck.
A 45-year-old Caucasian man was then arrested at around 6:45 pm local time.
While the motel is the main crime scene, local reports suggest there could be as many as five different crime scenes.
Mass shootings in Australia have been a rare occurrence since the country overhauled its gun laws in 1996, following the shooting in Tasmania that killed 35 people.
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