A landslip that destroyed a clifftop home and hospitalised a council worker was the second at the site in less than two weeks.
The house on Penny Lane at McCrae on the Mornington Peninsula collapsed shortly before 9am on Tuesday.
Mornington Peninsula mayor Anthony Marsh said there was minor landslip in the early hours of January 6 at the $2 million property, which prompted the owner to contact authorities.
"We had a geotechnical engineer come out and assess the site 24 or 48 hours after (the slip) and prepare a report and the site was deemed unsafe," he told AAP.
"Since then, we've spoken to the owners and to the insurers to list issues and have notified recommendations, and over the past sort of week, our staff have been there regularly, just doing investigations about the site.
"But had we not seen that, who knows what could have happened."
Mr Marsh confirmed the man, aged in his 50s, who suffered lower body injuries after being forced to jump from the second storey of the house, was a council worker doing an inspection relating to the earlier slip.
More than half a dozen properties surrounding the house have been evacuated until at least Wednesday night.
"Those investigations are ongoing, but there's obviously unstable land, so we need to work out exactly what's going on there," Mr Marsh said.
"It's devastating for the owners and it must be a huge concern for the close residents around."
University of Melbourne geomorphologist David Kennedy said building heavy structures such as houses on top of sea cliffs destabilised soil and could trigger slides.
"That can happen by putting weight on top of the cliff, it can also happen by building on the cliff face itself or even at the base of it," he said.
"The debris supports it and once you remove it that starts to make things a lot more unstable."
Local resident Tanina Osborne and her husband had just finished their morning beach swim when they heard a "horrible sound".
"I heard this really, really loud rumbling and like a crash," Ms Osborne told AAP.
"So my husband and I ran across the road and I saw that this house had tumbled down the hill - I've just never seen anything like it."
An advice alert for the incident warns the landslide could continue to move for days.
Multiple nearby homes remained a concern and were being monitored by authorities, State Emergency Service operations manager Chris Gregory said.
"A couple of them were vacant holiday homes and others had residents who were working with councils and other agencies to make sure they have a safe place to go," Mr Gregory told ABC Radio Melbourne.
Authorities have disconnected utility services in nearby properties as they assess the area for danger and the Nepean Highway has been closed between McCrae and Dromana.
Other houses in the area had reportedly been deemed unsafe in the past year, Ms Osborne said.
"I think that entire hill is going to have to be looked at," she told AAP.
"It would be an engineer's nightmare."
Ms Osborne said a water outlet near their daily swimming spot had been gushing into the bay three weeks earlier because of a water main issue on a road above the landside.
"That could have contributed as well, I don't know," she said.
"I'm not an expert, but you know that whole hill just has a lot going on."
