DARWIN, Australia - A gunman has been arrested after killing four people and wounding several others on Tuesday in the northern Australian city of Darwin.

Prime Minister Scott Morrison said a suspect was in custody.

"This is a terrible act of violence that has already, I'm advised, taken the lives of four people," Morrison told reporters in London, where he was on a visit to take part in D-Day commemorations.

"Our advice is that this is not a terrorist act. There is nothing to suggest that that is the case whatsoever."

Four men have been killed and one woman wounded, police said.

The 45-year-old man taken into custody following the shooting had been released from prison on parole in January and was wearing a monitoring bracelet, Northern Territory (NT) Police Commissioner Reece Kershaw said.

"He is an individual who's well known to police and has a number of interactions adverse with the police," Kershaw said.

"Today, June 4, 2019, has been a devastating day in the Northern Territory," NT chief minister Michael Gunner told reporters.

"Five crime scenes, four people deceased, one injured. This is not the Darwin we know," he added.

A man fired a pump action shotgun at the Palms Hotel in the Darwin suburb of Woolner in the late afternoon, Australian Broadcasting Corporation reported.

"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," witness John Rose was quoted as saying.

Another witness said she helped a bleeding women "with holes all in her skin" after a boyfriend carried the victim from the same hotel.

Police said the attacker went on a shooting spree in five different locations using a vehicle between sites that included pubs, a park, and a shop.

The alleged gunman remained at large in the tropical city of 100,000 for an hour before he was apprehended.

An ABC reporter said she saw police tackle and taser the suspect at a busy intersection.

Kershaw said the suspect was armed with a shotgun, but could not confirm what type.

Pump action shotguns have been virtually banned from private ownership in Australia along with other rapid-fire weapons under the country's tough gun laws designed to prevent mass shootings.

Two people were taken to the Royal Darwin Hospital with gunshot wounds and both were in stable condition, a Health Department statement said.(FA)