The seven cases takes the total number in the cluster to 104.
A record 60,184 people came forward for testing in the 24 hours to 8pm on Wednesday, with NSW Premier Gladys Berejiklian saying she nearly fell off her chair - "literally" - when she heard the staggering number.
"That many people and a 24-hour period is outstanding," Ms Berejiklian said on Thursday.
About 41,000 people were tested on the previous day.
The sources of the two other infections reported are still under investigation, as is the original source of the Avalon cluster.
Ms Berejiklian said health authorities are concerned about the possible emergence of a Sydney CBD cluster.
Three cases are now associated with Paragon Hotel Sports Bar at Circular Quay, including a positive case identified on Thursday who will appear in Friday's numbers.
People who were at the bar on December 16 at lunchtime for more than an hour are considered to be close contacts. Others who were there need to be tested as well.
Another new case is a person who works at an office in the vicinity of Hunter and Bligh Streets in Sydney's CBD, near the Paragon Hotel Sports Bar.
People near the busy CBD spots of Australia Square, the MLC Centre and Chifley Square should have a very low threshold for testing, NSW Chief Health Officer Kerry Chant told reporters.
"We are not out of the woods yet," she said.
Ms Berejiklian warned NSW residents to be "on guard" over Christmas because of the cluster. She encouraged people to get tested as soon as they feel the slightest symptom, even if it is Christmas Day or Boxing Day.
Meanwhile, a woman from the epicentre of Sydney's northern beaches COVID-19 cluster has been fined for breaking quarantine after police found her on the NSW South Coast.
The woman, 37, from Bilgola Plateau - in the midst of the Avalon cluster with the strictest lockdown - was issued a $1000 fine for breaching a public health order.
Police on Wednesday received reports a woman from the northern beaches had collapsed at a pizza shop at Sanctuary Point on Tuesday evening and had been treated at Shoalhaven Hospital.
The woman appeared to be experiencing symptoms – but refused to be tested – and left the hospital. Police found the woman at a Sanctuary Point home and spoke to her and three other occupants who were all directed to self-isolate.
The pizza store has closed for cleaning.
Bondi Icebergs Club and the MLC Centre food court in Sydney's Martin Place were on Thursday flagged by NSW Health as venues recently visited by people infected with COVID-19.
The latest alert also includes the Macquarie University Soccer Fields, a gym at Mona Vale, Alma Avalon Restaurant and De'assis Collaroy Cafe.
There are also numerous alerts for northern beaches buses which are listed on the NSW Health website.
NSW now has a four-tiered system of restrictions between Christmas Eve and Boxing Day and will return to previous settings on Sunday.
The approach has split the northern beaches into two communities, with the toughest conditions reserved for those living north of the Narrabeen Bridge.
All other state and territory borders are closed to people travelling from Greater Sydney.