Four people were killed Saturday in a foster home fire started accidentally by three children who were packing clothes in the basement for a planned runaway, investigators said.

The fast-moving blaze broke out shortly after midnight, killing two children and two adults. A fifth resident was seriously injured when she jumped from the top floor of the 21/2-story frame home in the city's Mattapan section."Three children were in the basement with lighted candles packing clothing for a planned runaway from the facility. One of the candles got upset accidentally. Some paint thinner, like everybody stores in their basement, contributed rapidly to the spread of the fire," said Boston Fire Department spokesman Ken Brunelle.

The children in the basement escaped safely before the fire moved up an interior basement stairway to the first floor, rear hallway and second floor.