NSW confirmed 12 new cases on Thursday as clusters associated with a Sydney CBD gym and two schools in the city's west rose to 52 and 12 respectively.

Three cases - a person in Parkes and two in southwest Sydney - have no known source.

Ms Berejiklian says she spoke to Queensland counterpart Annastacia Palaszczuk on Wednesday over the northern state's strict border measures.

The two leaders are at loggerheads over the border closure imposed by Queensland, which forces those coming from NSW without a valid exemption into 14 days of hotel quarantine at their own expense.

The restrictions came under fire last week after a Ballina woman pregnant with twins lost one of the babies after being forced to fly to Sydney for the birth.

The mother was told by northern NSW health officials she would have to go into quarantine under Queensland rules.

Ms Berejiklian said her conversation with Ms Palaszczuk was "polite and constructive" but she received no indication Queensland would ease its restrictions.

Ms Palaszczuk this week said border rules wouldn't change for at least another month.

Queensland chief health officer Dr Jeannette Young said on Thursday that NSW needed to pass 28 days without any COVID-19 community transmission before the border rules would be reassessed.

"The guideline that's been set by the Queensland government in relation to when they reopen their border is a pretty tall order," Ms Berejiklian said.

"I don't know anywhere on the planet where a society could function productively during a pandemic and get an assurance you're going to (get) zero cases of community transmission.

"If you have confidence in your health system, confidence contact tracing is something you can do within your state, there shouldn't be a reason for you to keep your border closed given the low rates of community transmission currently in NSW."

Ms Berejiklian said the two premiers also spoke about the difficulty Queensland-based doctors were experiencing crossing the border for work in northern NSW hospitals.

She said similar problems had been easily resolved on the closed NSW-Victoria border, for which the buffer zone will on Friday expand from 2.5km to 50km.

Health Minister Brad Hazzard said a number of northern NSW border facilities, including Tenterfield Hospital, were now devoid of doctors.

Ms Berejiklian said Ms Palaszczuk agreed her government would look into the issue.

In NSW, the cluster associated with the City Tattersalls gym has grown by three to 52, while the cluster linked to St Pauls Catholic College in Greystanes and nearby Girraween Public School has increased to 12. Both schools reopened on Thursday.

Meanwhile, another Sydney school has been shut for cleaning and contact tracing, after a case linked to the private school tested positive late on Wednesday night.

All staff and students at Regents Park Christian School are advised to monitor for symptoms, but those who attended after-school care on Monday and Tuesday must isolate for 14 days.

The case will be included in Friday's case numbers and is linked to a previously reported case.

NSW Health has also issued an alert for a church service at Life in the Spirit Ministry in Prestons, with anyone who attended on August 30 required to self-isolate for 14 days.

The new cases come after the Rail, Tram and Bus Union in NSW called for the appointment of marshals on public transport to enforce COVID-safe regulations.

Australian Associated Press