SYDNEY (REUTERS) - Australia can proceed with its reopening plans when the country reaches 70 per cent to 80 per cent vaccination levels, the government's pandemic modelling adviser said, even as some states hinted that they may not ease border curbs if Sydney fails to control its Delta outbreak.

The Melbourne-based Doherty Institute said the country's focus must shift to limiting the number of Covid-19 deaths and hospitalisations, from its current zero-cases strategy, when at least 70 per cent of the country's population above age 16 are fully vaccinated.

"This level of vaccination will make it easier to live with the virus, as we do with other viruses such as the flu," it said in a statement late on Monday (Aug 23).

"Once we reach 70 per cent vaccine coverage, opening up at tens or hundreds of cases nationally per day is possible."

Currently, 30 per cent of Australia's adult population have been fully vaccinated while 53 per cent have had at least one dose.

Australia in July unveiled a four-stage plan back to greater freedoms with higher vaccination rates.

But Queensland and Western Australia states flagged that they may not stick with the agreement as it was framed when case numbers in Sydney were much lower.

Prime Minister Scott Morrison acknowledged the concerns of some states over the Sydney outbreak but said "forever" lockdowns will do more harm than good to the country.

"It doesn't matter whether it's 30 cases or 800 cases, the conclusions are the same, and that's what the Doherty Institute said... we can do this safely and we do need to do it," Mr Morrison told Nine News on Tuesday.

Australia has suffered less from the coronavirus pandemic than many other developed countries with about 44,600 cases and 984 deaths.

But a third wave of infections from the Delta variant has plunged Sydney and Melbourne, its largest cities, and capital Canberra into a weeks-long lockdown.

Sydney, the worst-affected, has reported rapid growth in new case numbers as state officials pivot to a faster vaccine rollout strategy.

"Let us focus on the vaccine rates because that is what will determine how we can live moving forward," New South Wales (NSW) state Premier Gladys Berejiklian said.

Ms Berejiklian, who had promised more freedoms for the fully-vaccinated once total doses topped 6 million, said the state has crossed that milestone and changes will be announced later this week.

Some 59 per cent of people in NSW have had at least one dose, while 31 per cent are fully vaccinated, slightly above the national numbers.

New South Wales reported 753 cases, down from 818 on Monday, although daily infections continue to linger near record levels.

Seventy-four deaths have been reported from the latest outbreak, although the rate of deaths has slowed from last year.

Neighbouring Victoria, struggling to contain its outbreak, expanded access to the Pfizer shots from Wednesday to anyone over the age of 16 to help reach a goal of a million doses over five weeks.

Fifty new locally acquired cases were detected in the state on Tuesday, down from 71 a day earlier.