Girl stabbed in back during Sydney robbery

A 14-year-old Sydney girl had been late-night shopping with her boyfriend when she was stabbed during a struggle with an attacker, who fled with her backpack.

They were returning to a Blacktown home about 8.30pm on Thursday when they were confronted by a large man.

Her 15-year-old boyfriend says the alleged attacker pulled out a knife, demanding the girl hand over her backpack, which contained only a small amount of money.

Police say there was a short struggle as the girl tried to hold on to her belongings before she was stabbed in the back.

"He ran off with the bag and she just dropped to the floor," the boyfriend told the Seven Network.

Neighbours chased the man until they lost sight of him and called police.

"It's a pretty callous attack," Detective Inspector Paul Tickner told reporters in Sydney on Friday.

"The description of the male, he is Maori - Pacific Islander. He was a large build with a black, bushy beard wearing dark clothing."

Paramedics treated the girl at the scene before taking her to the Children's Hospital at Westmead where she received stitches for the wound.