Northern Territory Police are calling for witnesses in relation to an alleged aggravated assault which occurred yesterday afternoon.

At around 3:30pm, a male victim was allegedly assaulted by a 51-year-old man at Palmerston Bus Exchange. St John Ambulance located the victim unconscious and unresponsive and he was transported to Royal Darwin Hospital where he remains in intensive care.

Transit Security Officers held the 51-year-old in custody until police arrived. He was arrested by police and remains in custody.

Detectives from the Serious Crime Squad are investigating.

Any witnesses or anyone with information is urged to contact police on 131 444 or Crime Stoppers on 1800 333 000.