Sydney's St Vincent's Hospital has sent a further 995 people negative test results when their results have not yet been determined.
Pathology clinic SydPath issued its second apology in 24 hours for the latest error that caused a premature text message to be sent to those tested on 23 and 24 December.
"All of these people have been contacted and advised of the error," they said in a statement on Monday.
"They have been advised they will receive their accurate test results by tonight (Monday).
"Once again, we are sincerely sorry for this error and acknowledge the significant impact it has had on those involved."
The company said "a specific human error" was behind the inaccurate text notification, adding that procedures have been put in place "to ensure this cannot happen again".
It comes after SydPath confirmed on Sunday that more than 400 people who attended clinics throughout Sydney, including the Bondi Beach drive-through site, were incorrectly advised they had tested negative to COVID-19 when in fact they had tested positive.
The company said the latest error was uncovered by an emergency response team during the investigation into how the initial mistake occurred.
It said a large increase in demand at PCR testing clinics had added pressure to the capacity to turn around the results in a timely manner.
"This event comes at a time of unprecedented COVID-testing activity and SydPath’s people, as with all pathology teams throughout NSW, are working around the clock to respond."
Rise in COVID-19 patients in hospital
NSW Health is urging people to only get tested if they have COVID-19 symptoms, are a household contact or have had a high or moderate risk of exposure, in an effort to ease pressure on testing clinics.
It comes as the number of people in hospital with the virus has climbed to 520 - having doubled in the past week.
Some 55 people are in intensive care and 17 are ventilated on Monday as the state reported another three deaths.
Among them was a man in his 80s who became the state's first Omicron death, NSW Health says.
The man acquired his infection at the Uniting Lilian Wells aged care facility in North Parramatta. He was fully vaccinated but had underlying health conditions.
Another man in his 80s and a woman in her 90s also died.
COVID-19 restrictions re-imposed
With infection rates rising, NSW has reverted to restrictions scrapped less than two weeks ago.
Hospitality venues return to the one person per two-square metre rule and QR codes are compulsory from Monday.
NSW Health Minister Brad Hazzard has also revealed the government is "in deep conversation" about lifting isolation requirements for health workers exposed to COVID-19 to stem looming staffing shortages.
They would wear fitted P95 masks and full personal protective equipment, Mr Hazzard said.
NSW Labor health spokesman Ryan Park says the testing chaos and hospital staffing woes are evidence of a government without a plan to manage the latest spike in infections.
He wants the government to lobby for support from the Commonwealth or other states, which during other stages of the pandemic has come in the form of extra nurses and defence force members.
More than four in five NSW residents aged between 12 and 15 are now fully vaccinated. This increases to 93.5 per cent for people aged 16 and over.
Additional reporting: AAP
