NSW has confirmed 18 more local cases of coronavirus from nearly 60,000 tests to 8pm Sunday – figures that have raised hopes among state authorities.

“That is a great result and something we obviously want to see continue because the more testing we have, the more confidence our health experts have that they are capturing all of the cases in the community that may have been bubbling along for some days,” Premier Gladys Berejiklian said.

Monday’s figures came after 30 infections were reported on Sunday.

Only six of the latest cases are in people who were isolating throughout their infectious period, while three were isolated for part of the period.

Ms Berejiklian said 17 were linked to existing Sydney clusters, with the last “in the vicinity”.

However, she warned that case numbers could still rise considerably in coming days because of infectiousness of the Delta strain of the virus, which prompted the two-week lockdown of greater Sydney.

“The cases we are seeing today are a reflection of what may have occurred in the previous week and obviously there is a lag time,” she said.

“While the numbers today are less than the numbers yesterday, we have to be prepared for the numbers to bounce around and we have to be prepared for the numbers to go up considerably.”

NSW authorities say of 24 of 30 people who attended the West Hoxton birthday party a week ago – dubbed a “super-spreader event” – have caught the virus. None of the 24 were vaccinated.

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Chief health officer Kerry Chant said NSW needed at least five more days to see its case numbers turn around definitively.

“The restrictions came in towards the end of last week, there were other mitigations earlier on, but the cases we have now reflect exposures that occurred five days ago,” she said.

“If you are a close contact … please follow the health advice, stay in there for the 14 days, get the test, and follow the health advice. That will give us the greatest chance to achieve no community transmission as quickly as we can.”

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There were also new local COVID infections in other states and territories on Monday.

Northern Territory Health Minister Natasha Fyles confirmed six infections from 900 workers linked to the Granites Mine near Alice Springs, with more expected.

“We’ve gone up to six cases,” she told ABC radio on Monday.

“It is moving quite quickly and that number is likely to rise today. We’ve said to Territorians to be prepared for that.”

Queensland confirmed two new local cases on Monday, including the mine worker linked to the NT outbreak whose case was reported on Sunday.

Queensland will mandate masks outdoors in Noosa, Sunshine Coast, Ipswich, Logan, Redlands, Brisbane, Gold Coast, Scenic Rim, Lockyer Valley and Somerset local government areas from 1am Tuesday amid rising concerns about the spread of the virus.

The state has also introduced a host of other restrictions, including caps on numbers in venues.

Chief health officer Jeannette Young said the capacity for ticketed and seated events would not change, but she remained concerned.

“We’ve got enormous risks throughout our state,” she said.

Victoria had its second day in a row without local cases. But Premier Daniel Andrews – on his first day back at work after a back injury – has flagged further border restrictions will be announced later on Monday.

South Australia has already closed its borders to all states and territories, except Victoria and Tasmania.

Western Australia has tightened its border for residents of Queensland.

WA’s Perth and Peel districts are in lockdown after a local woman was confirmed with the virus after returning from Sydney. It is yet to provide an update for Monday.

All states have locked out Sydney residents.

Prime Minister Scott Morrison called a meeting of the national security committee of federal cabinet on Monday to discuss the outbreaks.

He will meet state and territory leaders at national cabinet on Monday night.

Treasurer Josh Frydenberg, who sits on the national security committee, said it would receive a briefing from Australia’s chief medical officer.

Mr Frydenberg said details about the latest developments would help inform decisions about vaccines and logistics.

But asked repeatedly what the national security committee could actually do, he did not give a firm answer.

Mr Frydenberg said the committee’s deliberations would feed into a national cabinet meeting to ensure consistency around state border closures and restrictions.

“Bringing the leaders together and hearing the most up to date information is important to align the responses,” he told ABC radio.

“The Prime Minister is also talking to state and territory leaders about the importance of ensuring workers in some of these facilities where the vulnerable cohorts are are vaccinated as well.”

Mr Morrison is expected to push state and territory leaders to make vaccines mandatory for aged care workers.

National cabinet will also discuss quarantine practices, including a ban on accommodating low-risk domestic travellers next door to high-risk international arrivals, which triggered an outbreak in Queensland.

They will also discuss testing and vaccinating those directly and indirectly working in the system, and introducing post-quarantine testing on day 16 after people emerge from isolation.

Vaccine stocks and the national rollout will be canvassed, along with federal supports available for aged-care responses and pandemic disaster leave payments.

-with AAP