Two women suffered head injuries after allegedly being assaulted by a woman who demanded money in a Phillip carpark last week.

Police say the women were walking through a carpark near the corner of Ball and Corinna streets about 9.40pm on August 26 when they were approached by an unknown woman.

The woman allegedly demanded money before assaulting them, causing head injuries to both.

Police have been unable to identify the alleged attacker and believe people near the busy intersection may have witnessed the incident.

Anyone who witnessed the assault or has dash-cam footage from the area is urged to contact police via the Crime Stoppers ACT website.

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