A threatening note has been attached to the front fence of a house that was engulfed by flames in Melbourne's east overnight.

A vacant house in George Street, Doncaster, that was due to be auctioned on Saturday was fully alight when fire crews arrived about 10:00pm on Friday.

Crews found a note with a symbol associated with Islam at the top and a message that, in part, said "ALERT ... your time has passed".

It also said: "Only the beginning more to come here or homeland, your next move will determine our next attack.

"We strike above the neck."

Detective Senior Sergeant Ian Shepherd said police were investigating if the note and the fire were linked.

"The investigation will look into whether or not that's connected to the fire or not. It's possible that it's not," he said.

"But it's certainly of interest to the investigation and the subject on that note is of interest as well."

The real estate agency involved in the sale of the house said it was shocked to hear the property was at the centre of an arson investigation.

One agent said there had not been any trouble before last night.