As the attacker held a knife to the throat of an 82-year-old woman and demanded her handbag, her 89-year-old friend hit the offender over the head with her own handbag at the shopping centre carpark in Malvern.

A passer-by came to their aid and the attacker ran from the carpark empty-handed.

A Victoria Police spokeswoman said the two women and their friend, 71, had been shopping at a bottle shop in Dandenong Road before walking back to their vehicle in a multi-level carpark in Drysdale Street about 3.15pm.

The women passed a stolen silver Mazda coupe parked on the ground level, with two men inside playing loud music.

Police said the "scruffy" passenger got out of the vehicle and threatened the Glen Iris women with a knife before her friend stepped in.

A Glen Iris man in his 40s then came to their aid and the bandit ran away.

The 82-year-old woman received a small cut to her hand, which did not require medical treatment.

The men were last seen in a silver Mazda coupe, registration TOA 542.

The offender is described as about 180 centimetres tall, aged 30 to 40, with a solid build. He was unshaven, scruffy and wearing a black duffle coat and grey baseball cap.

Detectives have urged anyone who saw the attack or anyone with information to contact Crime Stoppers on 1800 333 000 or visit www.crimestoppers.com.au

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