NSW Health said investigations were still ongoing into how a man in his 50s contracted the virus, before passing it onto his wife.
Most restrictions will remain in place across Greater Sydney (including Wollongong, the Blue Mountains and Central Coast) until 17 May.
From Monday, customers of retail and hospitality venues will be able to shop without wearing a mask, however public-facing retail staff must continue to do so.
In a statement, NSW Health said restrictions would remain in place "to safeguard the community and reduce the risk of further transmission" while investigations continued.
"NSW Health has not identified how the initial case … was exposed to COVID-19, which suggests he acquired the infection through brief contact with a currently unidentified person who was infectious in the community," the statement said.
NSW Premier Gladys Berejiklian tweeted her thanks to the public for their "patience" while contact tracers worked to identify the "missing link".
NSW recorded six new overseas-acquired cases to 8.00pm last night, while a previously reported overseas case has been excluded after further investigations.
This afternoon's Covid-19 briefing from New Zealand's Health Ministry said flights to and from Sydney were set to resume at midnight tonight, "subject to no further significant developments".
"This aligns with the lifting of NSW restrictions at 12.01am on Monday 10 May 2021," the briefing, which was issued prior to the NSW announcement, stated.
New Zealand public health officials said the risk to this country remains low, as there is no evidence to suggest widespread, undetected community transmission in New South Wales.
More than 5500 people who have arrived in New Zealand from New South Wales since Friday last week have been contacted by health authorities and provided with advice.