Police vehicles outside scene of shooting. (CBC)

Toronto police say they will "leave no stone unturned" in their hunt for the gunman who shot a five-year-old girl on Thursday night.

Someone outside fired shots and the child was hit in the chest as she stood inside her home, near Lawrence Avenue West and Weston Road.

At least one of the bullets went through a window of the family's ground-floor apartment and struck the girl in the chest.

She was rushed to Toronto's Sick Children's Hospital where doctors found the bullet had struck her lung. Despite the seriousness of the injury, the hospital said she is in stable condition.

"We're going to leave no stone unturned until we find who has done this," said Staff Sgt. Karen Smythe. "This is horrific."

Apparently, the gunman had been inside the family's apartment at 5 Bellevue Cres. before the shooting happened at around 8 p.m. According to police, he fired several shots at a group of people gathered on the patio from the two guns he had with him.

Police say they are investigating whether the incident is gang-related.

"I don't know so much about a turf war, but that is one direction that our inquires are taking us as far as gangs are concerned. Because not too many other people are walking around with guns and this fellow apparently walked in there with two of them," said Staff-Sgt. John Matthews.

"That's why we're appealing to the public to come forward, because especially with a five-year-old girl someone has to step forward and tell us who's doing this."

It's not the first time a child has been the innocent victim of a gun crime in Toronto.

In August 2005, four-year-old Shaquan Cadougan was shot in his knee, hip and thigh during a drive-by shooting on Driftwood Avenue.

In another incident in 2003, a five-year-old boy was shot in the face as he was walking home from the Molson Indy.