Urgent investigations into the source of the infection and contact tracing are underway, said the state health department, Xinhua reported. 

It was reported that the patient hadn't travel overseas recently, and he didn't work in a hotel quarantine, border or health role. 

NSW Chief Health Officer Kerry Chant voiced concern as the man had a high viral load, suggesting he was potentially highly infectious. His close contacts are being contacted, tested and isolated and genome sequencing is underway to find out the undetected transmission links. 

"In this case, we're really interested in how this person acquired the infection to understand the broader risk in the community," Chant said. 

"Understanding the source will be really important to understand how many cycles we have seen in the community that we haven't recognized yet." 

NSW authority named a list of venues concerning where the man visited and urged people who attended at the times specified to get tested and isolate immediately. 

NSW Premier Gladys Berejiklian said she expected more cases would be detected. 

"Our response would be proportionate to the number of cases that are established, the geographical location of the cases and whether or not they are in isolation," she said. 

She also urged the public to keep alert and take preventive measures. 

"We have to maintain our social distancing. We have to make sure we have good hand hygiene. We need to get tested with the mildest of symptoms, and very, very importantly and significantly, we need to use the QR codes."