Fire-fighters rescued two occupants, a man, 41, and woman, 38, from the house in Kneebone Street, Ararat about 12.30am.

Ambulance Victoria spokesman John Mullen said Ararat paramedics took the two people to Ararat and District Hospital before they were transferred to Ballarat Base Hospital.

Mr Mullen said both people were suffering from smoke inhalation.

"An Adult Retrieval Team, with a specialist doctor and senior Mobile Intensive Care Ambulance paramedic, went from Melbourne to Ballarat by road ambulance to get the man and transport him to the Alfred Hospital," he said.

"He is in an induced coma and has had a tube inserted to assist with breathing."

A Ballarat Health Services spokeswoman said the womanremained in a stable condition at Ballarat Base Hospital late yesterday.

Region 16 operations officer Ian Morley said Ararat Criminal Investigation Unit detectives and CFA fire investigators were yet to determine to a cause.

"At this stage the fire is deemed to be suspicious," he said.

Mr Morley said three units from the Ararat fire brigade, with 20 fire- fighters, took about 30 minutes to contain the fire in the weatherboard house.

"There were people inside, so fire-fighters with breathing apparatus entered the building and rescued two occupants," he said.

"There was severe damage to the house, from fire and smoke. Fire- fighters spent about three hours mopping up."