Health Minister Brad Hazzard said 500 previously tested swabs of travellers who had returned to NSW since November 22 had been lab tested to ensure they did not contain the Omicron strain.
None of them proved to be the new variant but one requires further investigation.
All of the 271 cases recorded in NSW in the 24-hours until 8pm on Wednesday were the Delta strain.
While the spotlight was on the Omicron strain, people needed to remember Delta was still circulating and everyone should be cautious.
People in New South Wales are being urged to get booster shots to protect themselves from Covid
'We know this virus is dangerous, it does come out in some different forms,' Mr Hazzard told reporters on Thursday.
'Don't take it lightly.'
The jury is still out on whether the latest strain is more dangerous and could overwhelm hospitals, or merely be more transmissible and able to replace stronger variants.
Health NSW said at least two people with the Omicron variant have been in the community because they landed in Australia before quarantine rules changed on Saturday.
A woman in her 30s from the Central Coast and a man in his 40s from Cabramatta in Sydney's southwest, are both infected with Omicron and arrived on the same Qatar Airways flight from Doha a week ago.
Mr Hazzard said the Cabramatta community was on high alert but stressed the infected man had only visited one shop on Monday.
'There have been no further indications of transmission in that area,' he said.
'It is still wise for us all if we have any symptoms whatsoever, whether it is Cabramatta, wherever it is, if you have symptoms don't forget the basic rule to go and