Two men and two women have allegedly attacked and robbed an autistic man after luring him to the Chisholm shops car park on Monday.

ACT Policing is seeking witnesses to the robbery, and believe the attack occured between 3.30am and 4.10am.

Police say the autistic man was lured to the Chisholm shops car park, after receiving a phone call from an unknown person asking him to meet them there.

When he arrived two men and two women approached him and verbally abused him.

One of the men was carrying a knife and punched the victim a number of times before another man took his phone and wallet. The group then fled.

Afterwards, a passerby helped the man call an ambulance and he was taken to Canberra Hospital, where staff called police.

Police are investigating and looking for CCTV footage.

The first male is described as Caucasian, about 183cm tall, skinny with dark hair. He was wearing a white T-shirt and black shorts.

The second male is described as Caucasian, about 180cm tall, skinny with blonde hair. He was wearing a white T-shirt and blue shorts.

Police are urging any witnesses to contact Crime Stoppers on 1800 333 000, or via act.crimestoppers.com.au.