Four people were killed in a mass shooting Tuesday in the northern Australian city of Darwin, police said.

Northern Territory Police Commissioner Reece Kershaw said a 45-year-old Caucasian man was arrested and is being held in hospital after opening fire at multiple locations across central Darwin.

One woman is in hospital with non-life threatening injuries.

Kershaw said the first phone call to emergency services was received at 5:45 p.m. local time.

Police believe the suspect tried to hand himself in about an hour later by contacting the duty superintendent. "He asked to be placed into protective custody, which we did," Kershaw said at a press conference.

The motive for the shooting is still being investigated, but authorities are not treating it as a terrorist incident.

"I understand when an event like this occurs, especially considering recent global events, people's fears turn to terrorism. I can confirm that we do not believe this is a terrorism incident," said Northern Territory Chief Minister Michael Gunner.

Kershaw said the suspect is "well known" to police and was on parole, having been released from prison in January.

The police commissioner would not elaborate on how he was known to police, other than to say he "may have associated" with entities such as local motorcycle gangs.

One of the shooting sites was a motel in central Darwin.

Witnesses told the Australian Broadcasting Corp. that a man dressed in high-visibility workwear was seen firing multiple rounds into the doors of motel rooms.