A NSW Health statement said "initial testing strongly indicates" the woman is infected with the Omicron strain of COVID-19.

This fully vaccinated woman is now isolating at home, but had been to various venues in Wyong, Toukley, Wadalba, Ryde and Parramatta on Friday and Saturday.

NSW Health has listed those places as exposure sites. They include an Aldi supermarket at Toukley, KFC at Wyong and various shops at Westfield Parramatta.

This woman was an overseas traveller, who had recently arrived in NSW.

"When confirmed, this would bring the total number of confirmed cases of Omicron in NSW to five," the NSW Health statement said.

"The traveller, who is fully vaccinated, arrived in Sydney on flight QR908 from Doha to Sydney on November 25 and travelled by private car to the Central Coast.

"The traveller had been in southern Africa."

NSW Health Minister Brad Hazzard told 7News the woman was in her 30s.

"This particular lady came in before the new arrangements, that is transferring to a health hotel, so she has been out in the community and health is now investigating that," Mr Hazzard said.

"She has essentially been out in the Central Coast area."

A second person on the same flight was now in Broken Hill. NSW Health said initial testing indicated this person was "unlikely to have been infected with the Omicron variant".

"This person, who is fully vaccinated and asymptomatic, is isolating at home."

Everyone on the flight is considered a close contact and will need to get tested immediately for COVID-19 and isolate for 14 days, regardless of their vaccination status.

NSW Health is contacting all passengers and flight crew to advise them of their isolation requirements.

They can also call NSW Health on 1800 943 553 for further advice.

NSW Health said a number of venues were visited by the Omicron-positive woman in Sydney and on the Central Coast before NSW Health directed travellers from southern Africa to go into isolation.

Anyone who attended the following venues at the times listed is a casual contact who must immediately get tested and isolate until a negative result is received. They should monitor for symptoms and if any symptoms occur, get tested again.

Friday, November 26

Top Ryde Coles, Top Ryde Shopping Centre 9.30am to 10.45am.

Target: Westfield Parramatta, 10.45am to 11am.

H&M, Westfield Parramatta, 11am to 11.15am.

The Athlete's Foot, Westfield Parramatta, 11.15am to 11.30am.

JD Sports, Westfield Parramatta, 11.15am to 12pm.

Rebel Sports, Westfield Parramatta, 12pm to 12.45pm.

IGA, North Wyong, 6.15pm to 7pm.

Pizza Hut, Wyong, 7pm to 7.15pm.

KFC North, Wyong, 7.15pm to 7.30pm

Woolworths, Wadalba. 7.30pm to 8.15pm.

Saturday, November 27

Aldi Toukley, 4.45pm to 5.45pm.

Quarantine

NSW Health said Commonwealth measures meant all travellers arriving in NSW who have been in South Africa, Lesotho, Botswana, Zimbabwe, Mozambique, Namibia, Eswatini and Malawi during the 14-day period before their arrival in NSW must enter hotel quarantine for 14 days, irrespective of their vaccination status.

All fully vaccinated travellers who have been in any other overseas country during the 14-day period before their arrival in NSW must travel directly to their place of residence or accommodation and isolate for 72 hours, pending further health advice.

Any unvaccinated arrivals go directly into 14-day mandatory hotel quarantine.

All flight crew who have been overseas during the 14-day period before their arrival in NSW must travel directly to their place of residence or accommodation and isolate for 14 days or until their departure on another flight that leaves Australia, consistent with the current rules for unvaccinated flight crew.

Anyone who has already arrived in NSW who has been in any of the eight African countries within the previous 14 days must immediately get tested and isolate for 14 days, and call NSW Health on 1800 943 553.