Australia's New South Wales (NSW) state reported zero Covid-19 cases for a fourth straight day, but concerns about new infections remained as the missing link in a case that has reinstated restrictions continued to elude officials, according to Reuters.

Australia's most populous state on Sunday extended social distancing curbs in Sydney by a week after authorities could not find a transmission path between an infected overseas traveller and a resident in his 50s who tested positive last week.

“There has been a lot of work to identify how the transmission event occurred. Unfortunately, we haven't found that missing link,” NSW state Chief Health Officer Kerry Chant told reporters in Sydney.