It took twenty firefighters and four fire engines almost two hours to quell a blaze in a Coulsdon house on Wednesday.
The fire at 95 Chaldon Way started at 3.45pm and was not brought under control until 5.30pm.
Station manager Justin Coo said the fire started in an upstairs room. "We do not know at this time what caused the fire but an investigation is ongoing. There are no suspicious circumstances that we are aware of."
Neighbour Anais Druard said: "I was in the garden when my friend and I saw the entire back of the [house] billowing flames, which were two or three metres high. It all happened very quickly, they blocked off the road and at the front were four fire engines.
"The house owner was clearly distraught going back and forth, asking questions."
A London Fire Brigade spokesman said a man had left the property before crews arrived.
Neighbours believe that a couple live in the house, which was their family home.
Mr Coo confirmed no one was hurt as a result of the blaze.
Another neighbour, Paula Rains, said: "I feel horrible. It's a bit of a shock and I feel very sad for them.
"But no lives were lost and that's the main thing. You can replace and repair things, so long as no one was hurt."
Mr Coo urged people to make sure they have a working smoke alarm fitted in their homes.
He could not comment on whether there was a working fire alarm in this house.