It happened around 4:40 p.m. inside a home along the 700 block of North Marvine Street.
Police say an 11-year-old girl was playing with the device when an explosion occurred inside the home.
"One of the young ladies had come running out hollering and panicking saying that something exploded and the little girl's fingers were cut off," said Janice McDonald.
McDonald is a retired nurse, and she just happened to be passing by when she saw the chaotic scene.
"I just wanted to do what I was able to because I'm a retired nurse. I took an oath, don't panic, you have to help and aid and assist," she said.
Developing: police and bomb squad on scene on the 700 block of N. Marvine for some sort of explosion. pic.twitter.com/EPsME2mcnu— Mike Nik (@6abcmike) October 29, 2019
McDonald saw that the little girl's hand was bleeding and badly damaged.
"She was in a panic stage, but what I did was wrap her hand so that it could stop the bleed," she said.
The child was transported to the hospital where she's listed in stable condition.
Police say there's damage to the second-floor bedroom and drywall where the explosion occurred.
Earlier this summer, a 9-year-old girl suffered serious injuries to her arms, body and face when an illegal explosive device detonated in her hands inside her Kensington home.