Disabled Vic woman threatened with knife

A disabled woman has spoken of her fear after a knife-wielding robber knocked her off her mobility walker and demanded money in Melbourne.

The victim, aged in her 30s, says felt "very scared" and cried during the robbery in Springvale on Thursday afternoon, which ended when she handed over $100.

The man tried to grab the woman's bag as she walked home from the shops, knocked her to the ground and then pulled out a knife before riding off on a black BMX, police say.

"I'm very scared and I cry," the victim, who was not injured in the attack, told journalists on Friday.

Detective Senior Constable Ben Oliver said it was a "vicious" and "disgusting" attack on a particularly vulnerable member of the community.

Investigators have urged anyone who saw the robbery on Heatherton Road to contact CrimeStoppers on 1800 333 000.