Commuters who boarded the same Sydney bus as two confirmed COVID-19 cases have been told to immediately self-isolate.

Passengers on the X39 bus that left Pitt Street opposite Australia Square at 6.08pm on August 20 and arrived at Randwick's Clovelly Road at Carrington Road at 6.40pm are considered close contacts.

They all must isolate until midnight on September 3 and be tested for COVID-19 regardless of symptoms.

A previously reported case linked to Sydney's CBD cluster took the bus as did a second passenger who was confirmed as having the virus on Friday.

Both live and work in the same areas and disembarked at the same spot.

Up to 11 other passengers were on the bus during the trip and NSW Health is contacting all registered Opal card users on the bus, although one wasn't registered.

In another alert, people who attended Highfield Caringbah pub for more than two hours from 6 to 8.30pm on August 22 are also being told to immediately isolate and seek testing.

Other patrons there for less than two hours have been deemed casual contacts of a previous case, but should still monitor for symptoms.

Gym goers who used Randwick's Fitness First weights room on August 23 at 3.30 to 4.15pm have also been directed to self-isolate as close contacts of a known case.

Meanwhile, Reddam Early Learning Centre at Lindfield has been closed for cleaning after a staff member tested positive.

The staffer, who is a household contact of a case linked to the CBD cluster, worked for three days from August 25 to 27 while unknowingly infectious.

That case will be counted among Monday's figures.

It will take the number of infections linked to the CBD cluster to at least 29.

NSW recorded seven new virus cases on Sunday after two more members of a city gym tested positive.

Of the seven new cases diagnosed overnight on Sunday, five are linked to the fitness hotspot including a close contact of a prior diagnosed member.

One new case is among returned travellers in hotel quarantine, while a student at a western Sydney high school has also tested positive.

St Paul's Catholic College in Greystanes will be closed on Monday for cleaning, NSW Health said.

People who attended the City Tattersalls gym in the Sydney CBD between 8am and 2pm on August 19, 21, 23, 24 and 25 are now considered close contacts and must isolate themselves and get tested immediately.

Authorities are also investigating the source of an infection acquired by a staff member at the Surry Hills Police Cells Complex.

A further 12 locations, including several public transport routes and Virgin Active gyms on Pitt and Margaret Streets in the CBD, have been added to a list of locations visited by people with active infections.

Homewares shop, House, at Broadway shopping centre was also closed on Sunday after a customer with COVID-19 went to the store on August 24 at about 2pm.

Three Sydney schools that closed on Friday after staff members contracted the virus will reopen on Monday.

They include Homebush Public School, Double Bay Public School and Ryde Secondary College.

Australian Associated Press