THE trial of a man accused of killing three members of the same family by setting fire to their home in Cwmbran last year heard today how a "fireball" took hold of the house.

Carl Mills, 28, of no fixed abode, has denied killing his partner Kayleigh Buckley, 17, her mother Kim Buckley, 46, and Kayleigh's six-month-old baby Kimberley, by setting fire to their house at Tillsland, Coed Eva, in the early hours of September 18 last year.

Members of the Buckley family sat in the public gallery at Newport Crown Court on the first day of Mills' trial.

Mills, wearing a black suit and white shirt with no tie, slumped in his chair while the prosecution showed text messages on a screen facing into the dock, and frequently rested his head on his hand and closed his eyes.

Prosecuting, Gregory Bull QC described neighbours' valiant attempts to demolish a fence at the back of the Buckley home in order to rescue those inside, and said witnesses heard Kim Buckley saying that she was on fire.

Several people including Kim's mother Gwyneth Swain left the court in tears as Mr Bull spoke.

"The picture they saw can only be described as heart-breaking," he said. "Kayleigh was seen in the window of a smoke-filled room, crying for help for her and the baby. People urged her to jump but she wouldn't leave the baby.

"One neighbour was heard saying she had become stuck trying to get out. Neighbours heard Kim say hat she was on fire and within a few minutes there was silence from those people in the house."

The fire service arrived quickly but the fire, which Mr Harrington said was caused when a naked flame was put next to combustible material in the porch, was so ferocious that they have to leave.

The fire burned through three doors in the porch and entered the top of a ground floor window, where it burned the top of the curtains.

The carpeted stairs then caught fire and effectively became a chimney, he said, channelling the fire straight upstairs where it may have entered the cavity wall through a hole in a panel.

Tar insulation melted and added to the fire, and there was easy access to the loft through a hatch, he said.

"The fire caused the stairs to fall in, in no time at all, and created a fireball going up into the roof space and bringing it down on the bedrooms.

"The three victims did not have a chance," he said. "The defendant would have known that the stairs were an immediate threat."

The trial continues tomorrow at 10am at Newport Crown Court. Mills denies the charges against him.