An elderly man is in a critical condition and two more people are injured after what witnesses described as a random, unprovoked attack by a young man in north Canberra.

Key points: Three people were injured, one critically, in a random assault

Three people were injured, one critically, in a random assault Witnesses described seeing a young man "visibly affected by drugs" attack two couples as they exited their cars

Witnesses described seeing a young man "visibly affected by drugs" attack two couples as they exited their cars Police arrested the attacker after what witnesses said was a "brief struggle"

ACT Policing said officers were called to a serious assault in Palmerston at about 10:15pm on Friday.

One of the three victims taken to hospital was critically injured, an ACT Policing statement read.

That man was still in a critical condition this afternoon.

Police said the young man who attacked the victims was arrested and later also taken to hospital.

Witnesses, who did not want to be named, said the attack was on two elderly couples who were exiting their cars on returning to one of their homes.

They said a young man who was visibly affected by drugs had been hanging around the area before he randomly attacked the couples, who had not provoked him in any way.

They said three of the people were injured while a fourth person fled to the home of a neighbour, who called police.

One witness said the alleged attacker was arrested after a brief struggle with police.

Police described the alleged perpetrator as thin, Caucasian, in his late teens or early twenties with dark hair.

They said he was shirtless and shoeless, and wearing dark tracksuit pants.

Officers asked anyone who saw a young man in or near Palmerston last night, has information that could help or has relevant CCTV footage, to contact Crime Stoppers on 1800 333 000 or via the Crime Stoppers ACT website.

They are asked to quote reference number 6374403, and have the option to be anonymous.