A 50-year-old man is in hospital with a fractured skull after he was assaulted in Darwin's city centre on Sunday morning.
Police allege a 35-year-old male punched the man in the head five or six times before swinging him into a metal sign.
NT Police Duty Superintendent Louise Jorgensen said the man was in custody and was likely to be charged later this afternoon.
"He appears as if he's fractured his skull, he's conveyed to Royal Darwin Hospital with very serious injuries," she said.
The victim is expected to have surgery later today.
"Intoxication is believed to be a factor, and alcohol was also a fact in the assault in Wulagi in the early hours of yesterday morning," Superintendent Jorgensen said.
"We know one punch can kill, so we treat these things very seriously.
"All those injuries have the potential to be fatal."
Police said they were interviewing witnesses and reviewing CCTV footage from the Smith Street Mall.
The assault follows another alleged attack in Darwin's northern suburb of Wulagi in the early hours of Saturday morning.
The 28-year-old victim was taken to Royal Darwin Hospital.
The 38-year-old man has been charged with aggravated assault and was released to face court on January 9.