The New South Wales state government reported 38 cases in its capital on Thursday, pushing the case number of this Delta outbreak over 370.
Authorities said people were breaching lockdown rules by going to other households.
They have pleaded with residents to abide by the stay-at-home order.
"We just need people to stop interacting for this lockdown to work," said NSW Premier Gladys Berejiklian.
"Please stop visiting people indoors, outside your family, your household. Your immediate family means those you live with, it doesn't mean extended family or friends," she said.
She added that people with symptoms moving around the community were also fuelling the virus' spread.
Thursday's case numbers marked the city's highest single day caseload in 14 months.
Australia's biggest city, home to five million people, is under a stay-at-home order until 17 July. The neighbouring Blue Mountains, Central Coast, Wollongong, and Shoalhaven regions are also affected.
Under the rules, people are allowed to leave their homes for essentials like shopping, exercise and care-giving. Businesses such as restaurants offering takeaway and specialist retail shops remain open.