Premier Gladys Berejiklian said the case was"very dangerous"and an evolving situation,but the health advice was that further easing of restrictions could proceed on Monday.
"When you are welcoming 3000 Australians back every single week,and when we know the rate of infection is increasing in all parts of the world ... we have to remain ever vigilant,"she said.
The woman worked at Darling Harbour's Novotel Hotel,a quarantine hotel,between Saturday and Monday. She had also worked at the nearby Ibis Hotel last Friday,November 27. Both hotels are owned by Accor and share staff.
Genomic sequencing is under way to determine if the case is linked to a traveller quarantined at the Novotel,with the results expected by Saturday.
The woman's family was tested late on Wednesday evening and all returned negative results. Workers at the two hotels have also been asked to come forward for testing.
NSW Health issued a number of alerts for passengers on train services between Minto and Central and light rail services between Central and Darling Harbour between Friday and Monday last week which the woman travelled on while believed to be infectious.