At least four people have been shot dead by a gunman in Darwin, northern Australia, police say.
Eyewitnesses said the gunman entered a motel in an inner suburb of the city and opened fire in a number of rooms before fleeing.
Police responded at about 18:00 local time (08:30 GMT) and arrested the man an hour later.
Australian Prime Minister Scott Morrison said the shooting was not terror-related.
Police said they believed the man had acted alone and they were not looking for any other suspects.
Mass shootings in Australia have been a rare occurrence since the country overhauled its gun laws in 1996, in the wake of a shooting in Tasmania that killed 35 people.
What do we know about the shooting?
Northern Territory police duty superintendent Lee Morgan confirmed the fatalities, and said two more people had been injured.
The city centre remained in lockdown for an hour after the gunman fled the scene of the shootings, in the suburb of Woolner.
The gunman was reportedly carrying a pump action shotgun, and up to 20 gunshots were heard.
Witness Leah Potter told ABC News that a woman was shot multiple times in the legs at the Palms Hotel.
“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.
“I ran and got some towels and wrapped up her legs, she had little holes all in her skin on both her legs and she was bleeding everywhere.”
Another witness, John Rose, told ABC that he saw the gunman 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.
According to Australian news site news.com.au, police were treating the Palms Motel as the main crime scene. Reports suggested there may be fatalities at two other sites in the area – the Buff Club and Gardens Hill Crescent.
The deputy prime minister, Michael McCormick, said the authorities were waiting to hear more about the “circumstances surrounding this dreadful and tragic event”.
Australia saw its worst mass shooting incident in more than 20 years last year when seven members of the same family died in a murder-suicide.
More recently, a man was killed and three others wounded in a shootingoutside a popular nightclub in Melbourne in April.