The Harpoon & Hotel Harry in Surry Hills, Matinee Coffee in Marrickville and Tan Viet in Cabramatta have all been closed for deep cleaning and contact tracing.

Darlo Bar in Darlinghurst on Thursday night also confirmed it was frequented on July 26 by someone who has since tested positive to COVID-19. The bar will be closed for cleaning and reopened on Saturday.

A positive case, the same person who attended The Apollo restaurant in Potts Point, went to the Harpoon and Hotel Harry pub on July 26.

A person with the coronavirus went to the Marrickville cafe on July 26 and 27, while another was at the Cabramatta restaurant on July 23.

NSW chief health officer Dr Kerry Chant on Friday said authorities had found the COVID-19 link between the two Thai Rock restaurants at Wetherill Park and Potts Point - subsequently introduced to The Apollo.

She reiterated that despite the legal 20-person cap in NSW on indoor and outdoor gatherings, people should limit gatherings to 10 people.

NSW recorded 21 cases in the 24 hours to 8pm on Thursday from more than 25,000 tests, with the Potts Point cluster growing to 19 people and the Thai Rock Wetherill Park cluster reaching 94 people.

Eight COVID-19 patients in NSW are in intensive care, with four on ventilators.

"We know most transmission events occur in an indoor environment, we know household-type gatherings are more likely to transmit," Dr Chant told 2GB radio.

"Think twice about having those gatherings up to 20 and minimise your contacts with others and minimise social events and movements just at this period while we're putting out spot fires."

Hygiene marshals will be required at NSW gyms from Saturday to ensure equipment is cleaned, hand sanitiser is available and social distancing is maintained, while gyms will need to register a COVID-safe plan.

The uptick in Sydney cases has prompted Queensland to ban all Greater Sydney residents from entering the state from Saturday.

Meanwhile, the Australian Border Force has denied a report that one of its officers allowed Ruby Princess cruise ship passengers to disembark in Sydney in the mistaken belief they had tested negative to COVID-19.

The ABC's 7.30 program on Thursday claimed a senior ABF officer allowed 2700 people off the Ruby Princess, thinking they were clear of the coronavirus when they had only tested negative to the common flu.

In a statement, the ABF said its responsibility does not include preventing the disembarkation of passengers or crew for health reasons.

"Any misinterpretation by ABF officers of test results did not make a difference as to whether passengers were cleared to disembark the Ruby Princess ... human health is not the responsibility of the ABF," the statement said.

The Ruby Princess, which docked at Circular Quay on March 19, has been linked to hundreds of COVID-19 cases and more than 20 coronavirus-related deaths.

Public hearings of a NSW inquiry into the incident have concluded, with Commissioner Bret Walker SC to report back by mid-August.

Dr Chant on Friday declined to confirm the ABF had made such an error.

Elsewhere, three Sydney schools were closed for cleaning on Thursday after recording confirmed or possible coronavirus cases - Fort Street High School in Petersham, Freeman Catholic College in Bonnyrigg Heights and Mary Immaculate Catholic Primary school in Bossley Park.

The Fort Street High School case has since been confirmed negative.

Australian Associated Press