Sydney, Jul 21 (IANS): Australia's most populous city of Sydney has experienced an uptick of community cases, over half of which are still under investigation, with health authorities scrambling to regain control, the media reported.

In the 24 hours to 8 p.m. (local time) on Tuesday night, the state of New South Wales (NSW), the epicentre of Australia's current outbreak, recorded 110 new community cases, of which only 54 have been linked to a known case or cluster, Xinhua news agency reported.

Worryingly, just 37 of these new cases were in isolation throughout the entirety of their infectious period.

The number of unlinked transmissions raised concerns that NSW is losing control of the outbreak. Health authorities remain hopeful that contact tracers will be able to link the chains.

"Hopefully most of them will be linked eventually but there is concern that there are unlinked cases which mean that because it is so transmissible, people are not aware of who they have been in contact with," said NSW Deputy Chief Health Officer Jeremy McAnulty.

Still expecting a turnaround, NSW premier Gladys Berejiklian said on Wednesday that Sydney is yet to see the effects of restrictions tightened last Saturday.

"We obviously went into harsher conditions last week and we won't have a sense until this weekend and early next week what the result of those harsher restrictions have been and I just ask for everybody's patience," she said.

The premier dismissed modelling which predicted Sydney would not be prepared to exit lockdown until September.

"The modelling can't predict how many people will stay in their homes and not be mobile. It's just an indicator for what could happen and different modelling gives you different results," she said.

In regional NSW, three areas entered a seven-day lockdown from midnight Tuesday after a truck driver with Covid-19 visited the regions last week.

Deputy Premier John Barilaro defended it as the "right decision".

"It's a reminder to everybody that we in regional and rural NSW aren't somehow not going to be impacted by the current delta strain," he said on Wednesday.

In NSW, there are now 106 people admitted to the hospital with Covid-19, with 23 people in intensive care, 11 of which require ventilation.