Australia's Chief Medical Officer Paul Kelly on Friday declared that "nothing is off the table" in order to make up for a shortfall in Covid-19 vaccines.

Kelly urged Australians to remain confident in the country's coronavirus vaccine rollout after use of the AstraZeneca-Oxford jab was limited, reports Xinhua news agency.

Kelly and Prime Minister Scott Morrison announced on Thursday evening that access to the AstraZeneca-Oxford vaccine, which Australia has acquired 53.8 million doses of, would be limited for citizens under the age of 50 on the advice of medical regulators.

It came after the European Medicines Agency (EMA) advised that "very rare cases of blood clots" were a side effect of the vaccine.

Kelly on Friday said he understood that the announcement could undermine confidence in vaccines but reassured Australians that authorities were working to secure additional doses of safer jabs.

"Of course something like the announcements overnight can affect vaccine confidence," he told the Australian Broadcasting Corporation (ABC).

"The important thing is for the Australian public to know that as soon as we've known something, as soon as our expert advice from the Australian Technical Advisory Group on Immunisation (ATAGI) gives us the guidance on immunisation, we went out (and informed the public).

"We've made this preference for not using AstraZeneca in the under 50s on the basis of that safety concern but ... I would really urge people to make sure that they are lining up when their turn comes to get the appropriate vaccine."

Kelly and Morrison said that the Pfizer vaccine, which Australia has only 10 million doses of, is "preferred" for adults under 50 who have not already received their first dose of the AstraZeneca vaccine.

Thursday night's announcement is the latest in a series of significant blows to Australia's vaccine rollout, which has been delayed by supply issues.

On Thursday, Australia surpassed 1 million vaccine doses administered.

In January the government promised that 4 million people would be vaccinated by the end of March.

Kelly told the ABC that "nothing is off the table" as the government seeks to address vaccine shortfalls, flagging a deal with Moderna.

The federal government has previously agreed to acquire 51 million doses of Novavax's vaccine, which has not yet been approved for use by the Therapeutic Goods Administration (TGA).

"We are looking at all of those options right now. We know that Novavax, we have 51 million doses on order, but that is not yet approved by the TGA," Kelly said.

"The TGA will absolutely expedite that matter. And as soon as Novavax is ready to supply to Australia we will be going through those processes."

Despite Thursday's announcement that use of the AstraZeneca vaccine will be limited, biotechnology company CSL, which was contracted by the government to manufacture 50 million doses locally, said it would continue to produce it.

"CSL remains committed to meeting its contracted arrangements with the Australian government and AstraZeneca for locally produced AstraZeneca COVID-19 vaccines," the company said in a statement on Friday.