Kingaroy fire: Blaze that killed father and kids may have been caused by cigarette

A baby, toddler and man are dead and a woman and child are in hospital after a devastating house fire in Kingaroy, Queensland.

Bruce Fisher, two-year-old Conner and 11-month-old Bruce Jr were found dead after emergency services responded to reports of the fire at the Kingaroy Street home, in the South Burnett region, about 1pm yesterday.

Three passers-by have been hailed as heroes after locating four-year-old Zach in the burning home and pulling them out through a window.

The men hit the walls, doors and windows of the burning home to check for occupants, and spotted the child near a window.

"To do what they did was courageous," police officer Ronald Reynolds said.

Mother Sarah Bond, who is pregnant, came home to find the home ablaze. A neighbour told 9NEWS she was inconsolable.

Ms Bond and young Zach were taken to hospital who was said to be suffering emotional distress.

The cause of the fire is not yet known but it's understood Fisher was drinking and smoking when his partner Ms Bond left the house earlier that day.

"The house continues to smoulder and is too hot for police to conduct a full inspection of the premises in order to ascertain the cause," police said yesterday.

Detectives, forensic officers and fire specialists are investigating.