Australia looks set to expand the rollout of the fourth dose of COVID-19 vaccines as it battles a steady rise in hospital admissions from the coronavirus fuelled by the highly transmissible new Omicron subvariants BA.4 and BA.5.

The new subvariants have now become the dominant coronavirus strains in several countries, with pandemic experts warning they could lead to more hospitalisations and deaths because they spread more quickly than other coronavirus variants. 

Nearly 3,800 people are currently in hospitals in Australia suffering from COVID, the biggest count since early February, according to official data, when Australia endured its previous significant Omicron outbreak.

New South Wales, Australia's most populous state, warned it was experiencing a fresh wave of infections driven by the BA.4 and BA.5 variants. Meanwhile, Victoria said these have become the dominant strains in the state.

Prime Minister Anthony Albanese on Wednesday flagged Australia "will inevitably follow" many other countries in expanding the eligibility of the fourth dose. It began administering a fourth shot to people above 65 in March. 

People above 30 will be able to get a fourth vaccine dose soon, the Sydney Morning Herald newspaper said in a report citing two unidentified sources, with the country's immunisation advisory group to formally recommend the change by Thursday.

After largely containing the virus through tough border restrictions and snap lockdowns earlier in the pandemic, Australia began living with the virus late last year through a staggered easing of curbs after higher vaccinations.

Australia on Wednesday scrapped a rule that required international travellers to declare their COVID vaccination status, marking the end of another major restriction.

Australia, among the most heavily vaccinated countries against COVID, has so far administered two doses to 95% of people above 16. More than 70% have been given a third shot, official data showed.

This has helped Australia to restrict its COVID numbers. The total death toll rose above 10,000 on Sunday, but the rise has been far slower than in many other countries.