The blaze broke out at a Merritt Street home in Harristown, Toowoomba, at about 12.30am.

A neighbour from across the road told 9News he was awake at the time and called emergency services after seeing fire in one of the windows.

Within minutes the entire front of the weatherboard home was engulfed in flames, the neighbour said.

A 34-year-old father, 36-year-old mother and four children managed to escape the home.

However, a fifth child was unaccounted for, with firefighters unable to get inside the property in time to save their life.

It was confirmed this morning the child had died.

The fire has since been extinguished.

The mother and two of the children were rushed to Brisbane for urgent treatment and are reported to be in a critical condition, fighting for their lives.

The father and two other children are being treated in Toowoomba Base Hospital with serious injuries.

Neil Goodman, from the Queensland Fire Service, said crews faced intense conditions when they arrived.

“Crews were initially met with a wall of flame and significant heat. Crews had quite a difficult time getting access to the front of the building,” he said.

Investigations are underway to determine the cause of the fire, and anybody with information is urged to contact Crime Stoppers on 1800 333 000.