A teenager has been arrested overnight after the owner of a supermarket in Darwin's northern suburbs was stabbed to death on Wednesday afternoon.
Northern Territory Police confirmed shortly after midnight that an 18-year-old man had been arrested in relation to the death.
Assistant Commissioner Travis Wurst said the man had handed himself into the Palmerston police station.
"He's currently in custody and assisting police with enquiries," he told ABC Radio Darwin.
Earlier on Wednesday, an NT Police spokesperson said the owner of the Territory Friendly Grocer on Progress Drive in Nightcliff, 71-year-old Linford Feick was attacked with an edged weapon shortly after 5.15pm.
"It is alleged that an unknown male was stealing items from a supermarket," they said.
"A 71-year-old owner of the store allegedly confronted the male and asked him to return the items before the male allegedly stabbed him with an edged weapon and fled the scene on a bicycle."
The spokesperson said customers inside the shop provided first aid and called emergency services but Mr Feick could not be revived and was pronounced dead at the scene.
Assistant Commissioner Wurst said "police responded as quickly as we possibly could, within minutes of a call being received".
"Northern Territory police then enacted a surge mentality when it came to trying to identify and locate this male," he said.
"We identified him through some CCTV relatively quickly, and then considerable efforts were put in place, with multiple specialist teams flooding into the community.
"As a consequence of engagement with the family of this particular person, he handed himself into the police station."
Earlier, officers cordoned off an area in front of the store as plain-clothed detectives arrived and other store employees gathered outside, visibly shaken, while investigators took witness statements.
A woman who said she was inside shopping for bananas at the time of the attack told the ABC she saw a man approach a worker with a knife.
"The bad man [was] screaming at the front of the door and then they pulled out the knife," she said while gesturing toward her arm.
"After that, the worker was very pale in the face before laying down.
"Then, after 25 minutes, I heard they passed away."
St John Ambulance NT's Craig Garraway said there were a number of people who rendered first aid at the scene before police and paramedics arrived.
"I'd like to thank all them — some doctors and nurses and other bystanders who did everything they could to try and support that gentleman," he said.
"Unfortunately, their efforts were in vain."
Chief Minister Lia Finocchiaro said she stood with Territorians "in absolute grief about losing yet another member of our community to crime".
"There is a family who've lost a husband, a brother, a father, an uncle, a loved one, a community who's lost a friendly face, someone they love to go and see every day," she told ABC Radio Darwin on Thursday morning.
Ms Finocchiaro said she would have "more to say later today about the reform package we need to move urgently to do".
"I want to assure Territorians today that there will be very high visibility policing … particularly in retail," she said.
