Two fluff balls with bites bigger than their barks have been labelled "little heroes" after rescuing their owner from a would-be rapist lurking in a Melbourne cemetery.

RuPaul and Louie "viciously" attacked the unknown man as he held their owner to the ground and tried to pull her pants down at the Williamstown Cemetery.

Victim Kate, not real name, with her little heroes Louie and RuPaul at the Williamstown Cemetery Eddie Jim

Kate, who asked that her real name not be used, walks the shih tzu and terrier-cross through the cemetery most afternoons but was delayed on Saturday, June 29 until well after dark.

The man attacked from behind at about 8.30pm as Kate waited for the dogs to come back from chasing a rabbit.

But it wasn't long before the dogs turned the tables.

"They viciously attacked him – growling, biting and, I think with my screaming and the struggling, it made him stop," Kate said on Wednesday.

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"I keep thinking about what would have happened if they had've gone off or not come and done anything, so I think they saved me.

"You wouldn't know [to look at them] but they're extremely protective and will probably bite your ankles."

The man fled in the direction of KC White Reserve on Park Crescent and is still on the loose. It is not known if he was injured in the attack.

"It got to the point where he was trying to take my pants down and I was pushed down into the mud, unable to really move," Kate said.

Kate with Louie and RuPaul Eddie Jim

"By that point, when he had gone that far, my screams got louder ... and the dogs were going for it.

"It was just an instant release and by the time I got up and turned around he was running away."

Kate, who lives nearby, was so traumatised by the attack she moved out of home for a week.

Detective Senior Constable Jenna Sladek said the "little heroes" had done their job and now it was the public's turn.

“We know people congregate at the cemetery at night so we are keen to hear from anyone who witnessed the assault or may have been in the area at the time,” Detective Senior Constable Sladek said.

The attacker is described as having a large build and was wearing a black puffer jacket and white beanie.

The cemetery is popular with walkers and police have asked anyone with information to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppers.com.au