A 17-year-old was stabbed and critically injured after a 14-year-old girl's birthday party in Five Dock went out of control overnight.

The girl's grandmother, Christine Varricchio, said the birthday party was gatecrashed by older teenagers.

“She just tried to have a party with pizza, and all she bought was lemon squash and strawberry sarsaparilla,” Ms Varricchio said.

The girl’s mother was home and upstairs at the time, but could not hear what was happening because of loud music. The party was supposed to be low-key, with only a “handful” of invited guests, Ms Varricchio said.

A 16-year-old boy has been charged following a stabbing at the gatecrashed birthday party in Five Dock on Friday night.