The Tangara cluster now includes 25 cases, while Sydney Girls confirmed it learned of a new case in one of its students on Sunday morning.

It said a trial HSC examination scheduled for Monday would be rescheduled and students notified.

Students who attend the selective girls' high school commute from suburbs across Sydney, often via public transport.

A NSW Department of Education spokesman said the school was working closely with NSW Health to establish close contacts of the affected student.

"All staff and students are asked to self-isolate while contact tracing occurs," he said.

"Students will continue to be supported through existing learning from home arrangements while the school is thoroughly cleaned. Further advice will be issued tomorrow on when on site teaching and learning can resume."

Party buses investigated for protocol breaches

Police are investigating potential public health order breaches after being called to two separate incidents involving party buses on Saturday night.

A party bus operator who drove 43 people from Penrith to Sydney's CBD on Saturday has been fined for breaching restrictions.

Police were called to Wheat Road near Darling Harbour at 11.15pm on Saturday night due to "concerns about the way a bus was being driven".

The 25-year-old driver was given a $5000 penalty infringement notice and a 17-year-old passenger was arrested after a drug dog was brought on board and the girl was allegedly found with cocaine.

In a statement, NSW Police said officers also spoke to the driver about several underage passengers allegedly being intoxicated.

Police are separately investigating another party bus incident in north-west Sydney on Saturday night.

Police were called to Thornleigh about 11.30pm following reports of an alleged assault on board and found about 40 young people, aged between 16 and 18, were on the bus.

"The NSW Police Force is working with NSW Health and Transport for NSW to determine whether there have been any breaches of current Public Health Orders," a NSW Police spokesperson said.

New venues on high alert

NSW Health is advising that anyone who visited the following venues is considered a casual contact of previous cases and should monitor for symptoms:

• Crust Pizza in Concord on Thursday, August 6 between 4pm and 8pm or Friday, August 7, between 5pm and 9pm;
• Den Sushi in Rose Bay on Saturday, August 8 between 7.15pm and 8.45pm;
• Cafe Perons in Double Bay on Saturday, August 8 between 1pm and 2pm;
• Horderns Restaurant at Milton Park Country House Hotel and Spa in Bowral on Sunday, August 2, between 7.45pm and 9.15pm.

Anyone who visited these venues and develops COVID-19 symptoms should get tested and isolate immediately, NSW Health said.

"People who are infected and develop symptoms will generally do so within 14 days of exposure," NSW Health executive director Jeremy McAnulty said on Sunday.

The new cases bring the state's total COVID-19 case count to 3761.

Of those, there are 119 people being treated by NSW Health, including seven who are in intensive care units, five of whom are ventilated.

About 88 per cent of cases are being treated outside hospitals, Mr McAnulty said. Nearly 24,100 tests were conducted across the state on Saturday.

"COVID-19 continues to circulate in the community so maintaining very high rates of testing is really important so we urge anyone with even the mildest symptoms to come forward for testing," Dr McAnulty said.

The number of new locally acquired cases has been below 10 for the past four consecutive days, the first time this has happened since July 18.