It comes after SydPath, St Vincent's Pathology, advised more than 400 people infected with COVID-19 they were negative.
Now, a further 995 people have received an SMS from SydPath saying they were negative to the virus when the results had not been confirmed.
"The emergency response team investigating the cause of this error, has now identified approximately 995 more people, tested on 23 and 24 December, were prematurely sent an SMS advising them their test was negative when in fact their true result had not yet been determined," SydPath said in a statement.
"All of these people have been contacted and advised of the error.
"They have been advised they will receive their accurate test results by tonight."
SydPath has apologised for the mistake and said they have identified what occurred, and is related "to a specific human error".
"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," SydPath said in the statement.
SydPath medical director Professor Anthony Dodds read out a statement to the media on Sunday afternoon when the intitial mistake was revealed, blaming the "very large volume of tests that we've been contending with".
People are also waiting days for results, upsetting travel plans and leaving potential COVID-19 sufferers confined.
Premier Dominc Perrottet urged people yesterday to only get a PCR test if they are symptomatic or if they have been advised by NSW Health.
"I know there are long queues right across our state, so if you do not feel unwell there is no need to receive a PCR test. You are taking a spot in the queue from somebody who needs a test," he said.
"We just don't believe that the requirement of a PCR test for somebody who is not unwell is actually supportive of that view."
Three more deaths of people with COVID-19 were also reported, including the first known linked to the Omicron variant – a man in his 80s from Western Sydney.