SPRING VALLEY, Calif. -- An 18-year-old man's attempt to stoke a fireplace with gasoline in his grandparents' East County home ignited a fast-moving fire that trapped and killed his three young cousins, authorities reported Thursday.

Abbey Van Buskirk, 6, and her brothers, Andrew, 4, and Austin, 2, died Wednesday night as flames gutted the house in the 9000 block of Avocado Street in Spring Valley, according to the county Medical Examiner's Office.

The blaze erupted about 10:40 p.m., when the children's cousin, who was watching a movie on television with a group of friends, tried to stoke a dying fire in the home's fireplace by pouring gasoline on it, officials said.

One of the young man's companions, Cameron Bartlett, told reporters the gas spilled on the floor, setting it ablaze.

"And then it just started," Bartlett told 10News Thursday morning. "And the house was, like, gone in about, like, five minutes."

All the adults were able to escape after several of them tried in vain to save the three young siblings.

Neighbor Joanne Collier described hearing the children's shrieks as the house became engulfed in flames.

"It was a hysterical cry," she told 10News. "You know, you could hear them screaming, and it was just -- it was horrible."

It took firefighters about 15 minutes to extinguish the flames. They then found the bodies of the children in the charred ruins of the house, said Sgt. Everard Dayrit of the sheriff's bomb-arson unit.

The youngsters' cousin, whose name was not immediately released, was taken to the University of California, San Diego Medical Center in Hillcrest where he is listed in good condition.

The children had recently moved with their family to San Diego County from Texas, a coroner's investigator said.