A PORTABLE school classroom being used as a temporary home at Barfold was destroyed by fire on Wednesday night.
Fourteen firetrucks were called to the Mills Road property at about 7.30pm.
They found a portable classroom engulfed by flames, which was about two metres away from a home under construction.
The brother and sister living in the classroom were out at the time of the fire.
CFA operations manager Craig Brittain said they returned home while firefighters were packing up to leave.
"Early on there was some concern for the residents' safety when firefighters found a car parked out the front of the property with keys in the ignition," he said.
"Firefighters searched the property but found no one."
It took 11 crews from Castlemaine, Kyneton, Maldon, Redesdale, Langley-Barfold, Metcalfe, Malmsbury and Taradale about an hour to control the fire.
They were on scene until around 11pm.
Redesdale CFA captain Glenn Brown said the fire was fierce.
"The fire was visible from about three kilometres away," he said.
"It was fully involved when we got there. The roof collapsed early on."
He said the house under construction had only very minor damage to a drain pipe.
A police guard was at the scene yesterday.
The cause of the fire is still under investigation.
The fire was visible from about three kilometres away