COVID-19 alerts go out for a major Sydney shopping centre, gym, pub and popular bus route after thousands flocked to the beach to soak up the sun over the weekend

A Sydney bus route, a popular gym and a pub are the latest subjects of urgent public health warnings as a COVID-19 cluster in Sydney's CBD spreads.

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.

NSW Opposition Leader Jodi McKay has reiterated her call for Premier Gladys Berejiklian to mandate mask wearing for everyone on public transport.

'We now have an entire busload of passengers forced to self-isolate. Premier, please bite the bullet and make face masks mandatory on public transport. The dithering has gone on too long,' Ms Mckay tweeted on Monday.

The alert comes after enormous crowds flooded beaches across Sydney as the mercury soared to 23C on Sunday. 

Lifeguards used loudspeaker systems to try and encourage swimmers and sunbakers to practice social distancing but photographs showed crowds packed together like sardines on the shore. 

There are no restrictions on gathering in public or going to the beach in NSW, but Gladys Berejiklian has urged residents to try and stay 1.5metres apart and wear masks if social distancing is not possible.

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.

Over the weekend police kept an eye on social distancing at beaches as warm weather enticed people to hit the sands.

The coronavirus cluster linked to a gym in Sydney's CBD has grown to 29 infections.

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.

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

St Paul's Catholic College in Greystanes will be shut on Monday for cleaning, NSW Heath said on Sunday.

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

NSW deputy chief health officer Jeremy McAnulty said the Justice Health and Forensic Mental Health Network were taking appropriate health and safety measures.

'Contact tracing has been undertaken and the staff member is isolating.'

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.

A 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, around 2pm.

Anyone who visited the above locations is being urged to watch for symptoms.

Meanwhile, 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.

There are 66 active COVID-19 cases in the state, including six who are in intensive care, of whom three are on ventilators.

More to come