The incident unfolded at a complex on Bowman Street in Pyrmont about 4.50 am today.
Police were told a man had allegedly forced entry into the unit and stabbed the woman in the head before fleeing.
Paramedics treated her at the scene and she was taken to hospital in a stable condition.
The man and woman are believed to be known to each other, according to police.
Another woman and two children were also in the home at the time, but suffered no injuries.
Police have established a crime scene and commenced an investigation into the incident.
