Passersby rescue woman during attempted armed robbery at Melbourne ATM

Passersby rescued a woman after a stranger allegedly grabbed her as she waited at a Melbourne ATM and threatened her with a sharp object in the middle of the afternoon.

Police are now calling for help to identify a woman who they believe is behind the attack in South Melbourne last month.

The 47-year-old victim was allegedly standing in line at an ATM at the intersection of Clarendon and Dorcas Streets in South Melbourne about 4.25pm on August 25 when the incident occurred.

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An unknown woman allegedly approached the victim from behind and put her arms around the victim, while holding a sharp object to the victim's back.

The offender allegedly made demands for the victim to hand over money before several passersby intervened and dragged the woman away from the victim.

The offender managed to flee, running south on Clarendon Street towards Bank Street.

Detectives have now released an image of a woman who police believe will be able to assist with the investigation.

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The woman was believed to be approximately 25 to 35 years old with short black hair, about 163cm tall and wearing a black puffer jacket, black hat, shorts and runners.

She also had a tattoo on the left side of neck comprising of one or two words in calligraphy style writing.

Police are also calling for anyone who witnessed the incident, in particular those members of the public who intervened, to contact them.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au