The Smith family were awake and inside their rented home on School Hill when the drama unfolded yesterday at about 7am.
Val, 56, was in the kitchen when she heard what she thought sounded like a thunder clap.
Her son David, 20, was upstairs and called out to alert his mum and dad Ray, 56, about what was going on.
Mrs Smith said: “It was still dark outside and we thought the noise was the result of a tree coming down.
“As it became lighter we could see that most of the bank above had fallen into our backyard. It had landed right outside the kitchen and there was a tree stuck on the kitchen roof.”
It’s thought heavy rain could have caused part of the access road on Prospect Terrace to fall into the garden.
Mrs Smith added: “I suppose the tree and the bank came down and brought the rest of the debris with it.
“There is a great big gap in Prospect Terrace, which is worrying for them.”
Neighbours leapt to the aid of the family and called the fire service, who attended the scene, and calls were also made to Cornwall Council.
“We were really lucky – it could have been a lot worse.
“Hopefully we will not have to move out,” Mrs Smith added.
A Cornwall Council spokesman said it had made the area safe but because it was a private road it was not the authority’s responsibility to make repairs.