A disabled woman was robbed at knifepoint by a man in Springvale on Thursday, in what police have called "a vicious and disgusting attack" on a defenceless and vulnerable victim.

The woman, aged in her 30s, was walking home from the shops on Heatherton Road, about 4.30pm, when a man riding a bicycle approached her from behind.

She was walking with a mobility aid, which she needs to move about. Her handbag was hanging across the walker.

The man tried to grab her bag, and when the victim fought back, she fell to the ground.