New South Wales authorities are retesting thousands of COVID-19 swabs for the Omicron variant.
NSW Health will check 2000 positive COVID-19 swabs from recent weeks for signs of the variant.
This is to determine how long Omicron has been circulating in the state.
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NSW Health Minister Brad Hazzard said pathology has already retested 500 swabs from people who have arrived from southern African countries in the past two weeks.
"They have now completed 500 cases that have come into NSW since the November 22 and they've gone right back through the pathology and I'm pleased to say at the moment none of those proved to be positive to Omicron," he said.
Mr Hazzard added that authorities are currently investigating one case for the variant.
"We are looking at one particular case which we will need to do some more work on and we will make some announcements on that in the next few hours," he said.
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It comes after a man in south-west Sydney became the state's sixth infection of the strain.
The fully vaccinated man had recently visited southern Africa and arrived on flight QR908 from Doha to Sydney on November 25.
He was on the same flight as the Central Coast woman who tested positive to Omicron on Tuesday.
The man had spent the last six months in Nigeria, which is not one of the eight African countries subject to the border closure issued on Saturday.
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All passengers on the QR908 Qatar Airways flight have been directed to get tested and self-isolate for 14 days.
So far, only one of the seven Omicron cases in Australia are not in NSW.
The seventh is a case in quarantine in Howard Springs in the Northern Territory.
