Fire that burnt SA girl deliberately lit

A house blaze in South Australia that has left a young girl seriously burnt was deliberately lit.

A mother and her two young daughters escaped the fire at the Port Pirie West home on Thursday morning and police say they now believe someone lit it, possibly using an accelerant.

One of the girls was airlifted to Adelaide's Women's and Children's Hospital where she remains in a serious but stable condition, while her mother and her sister have minor injuries.