Fire officials say that a fire at a residence in south London was a dangerous situation as crews were faced with a "ball of fire" on the second floor.

"At that point we're concerned of smoke explosions and backdrafts.Fashovers are probably our biggest fear," said Fire Captain Tom Nicholson.

"Once we knocked the body of the fire down on the main floor we just advanced to the second floor where we were faced with another ball of fire upstairs," said Nicholson.

The fire began out around 4:20 p.m. Monday at a home on Country Club Drive in south London. Neighbours say it started in the rear of the home and quickly spread.

Fire crews used several hoses to knockdown the fire and prevent an adjacent residence from sustaining damage.

No one was injured in the blaze but the house was left gutted with a damage estimate of $600,000.

Following an initial investigation the cause of the fire remains unknown and the Ontario Fire Marshall has been called in to investigate.