SYDNEY • Police said at least four people were fatally shot yesterday in Darwin, the capital of Australia's Northern Territory, when a gunman went on a shooting spree in the city's main business district.

The police said a 45-year-old man has been arrested.

"The active shooter threat has dissipated," said Superintendent Gavin Kennedy of the Northern Territory police.

He added that the police were investigating at least five crime scenes in the city.

Prime Minister Scott Morrison said the attack was not believed to be terror-related. "Our advice is that this is not a terrorist act," he told reporters travelling with him on his first visit to London.

Witnesses told Australia's public broadcaster ABC that the gunman walked into Palms Motel in Darwin's Esplanade area just before 6pm, carrying a shotgun.

"He shot up all the rooms and he went to every room looking for somebody and shot them all up," said Mr John Rose, a witness. "Then we saw him rush out, jump into his pick-up and rush off."

Another witness said she helped a bleeding woman "with holes in her skin".

The shooting seemed to be Australia's deadliest since May last year, when seven members of a Western Australia family were found dead in an apparent murder-suicide. That was the country's worst mass shooting since the 1996 Port Arthur massacre in Tasmania, which left 35 people dead and led to a toughening of gun laws.

Experts define a mass shooting as the deaths of four people, excluding the gunman, in a single event.

Polls show more than 90 per cent support in Australia for the two-decade-old gun regime, but the country has been loosening its laws in recent years and gun sales are increasing.

AGENCE FRANCE-PRESSE, NYTIMES