NSW Premier warns household gathering restrictions unlikely to ease before Christmas

Ms Berejiklian said she was "always looking to push the boundaries to make life easier for our citizens" but that had to be balanced against public health considerations.

"We are looking very closely at what we can do over summer in relation to hospitality and the arts community in particular," she said.

The Premier also said she had no confidence in ever achieving the Queensland government's target of zero local COVID-19 cases for 28 days before border restrictions are abolished.

Queensland is off-limits to anyone who has been in Greater Sydney in the 14 days before wishing to enter the state.

The Queensland government has previously stated that NSW health authorities must record 28 consecutive days without community transmission, unless there is a linkage to a known source within 48 hours of the disease being diagnosed, before the border closure is lifted. If these conditions are not met, the 28-day so-called "border clock" will be reset.

On Tuesday, NSW reported its third consecutive day of zero locally transmitted cases, but Ms Berejiklian was downbeat about the prospect of stretching that streak to four weeks.

"I’m not worried about resetting the Queensland [border] clock because we'll never reach that target," she said. "I think it would be highly unlikely to go for 28 days during a pandemic and to be able to say we can identify every single source."

Ms Berejiklian said contact tracing was not always possible within a two-day period.

"Eventually they do manage to trace down every single case. Some could take hours, others take days and some could take weeks."

The most recent case without a known source was discovered in Moss Vale in the Southern Highlands on Friday and remains under investigation.

"I have been advised there are genomic similarities between the Southern Highlands case and other cases in south-western Sydney so we do know they're of a similar strain and there are those links," Ms Berejiklian said.

Five cases were detected in overseas travellers in NSW hotel quarantine in the 24 hours to 8pm on Monday.

Australia is on track for its third consecutive day of zero locally acquired cases nationally after Victoria recorded its 11th day in a row without a case.

There were 10,058 tests done in NSW in the reporting period, compared to 9499 on Monday. There are 70 active cases of COVID-19 in NSW, and only three of those are being treated in hospital.

Meanwhile, Sydney commuters will be able to receive real-time notifications about the capacity of train services under new technology being released.

The opt-in system will be available to registered Opal card holders who have the Opal app on their phones. Commuters will be able to receive alerts half an hour before their regular train to see how full it is.

NSW Transport Minister Andrew Constance touted the new technology as "a world-leading piece of innovation" that will be rolled out on buses and light rail at a later date.

Mr Constance again ruled out masks becoming mandatory on public transport, despite his pleas for people to wear them.

"I don't want to create a culture where we start having these big sticks waved to the community," he said. "We don't need to put punitive measures in place, fining people and denying them a service."